Top Ten Invasive Ornamental Plants You Shouldn’t Have in Your Garden

Without any bad intent many ornamental plants worldwide have been released into gardens and landscapes of their new homes, only to become serious invasive pests. Some were simple stowaways, others were brought as food, a few to purposely modify landscapes, and yet others simply because they were beautiful – it is this last group, the ornamental plants, I wish to address in this article.

With the advent of international exploration and trade, there also began the movement of exotic plants and animals across the planet. Early colonizers and traders at first brought useful plants, such as grains, vegetables, fruits and fiber crops to new lands, but in time ever more unusual and exotic species made their way as well. While both Asian and early American cultures had been trading in various plants for over a thousand years, movements of these was relatively slow and limited. It wasn’t until the Europeans with their ocean going ships did the flow of exotic species go from a trickle to a torrent across the world. And so began the age of invasive exotic species.

This flood of invasive species is well known these days and even makes the news frequently. In the USA we all have heard about Japanese knotweed overtaking disturbed land throughout the northern states, kuzu vines strangling acres of southern forests, cheat grass crowding out native grassland species in the western mountains, and hydrilla hopelessly clogging innumerable waterways.

Honeysuckle Vine
The Japanese honeysuckle vine, Lonicera japonica, is a well known invasive exotic weed the world over.

But there remains a real danger with regard to ornamental invasive plants – the desire to grow them regardless of the threat to natural systems and the species that these support. The truth is that many ornamental plants have been in cultivation for just a relatively short time, so well meaning gardeners could have ticking time-bombs in their midst and not even realize it. Moreover, once an invasive has entered a natural system it is hard to know the effect it is having on other species, or indeed the very physical elements such as water and soil.

The following list is just a sample of beautiful exotic pests that have already run rampant over native ecosystems or are threatening expand their range. Some may indeed to be found to be mere localized pests, or so limited by the type of habitat they can invade that their effect is not pervasive. In any event, it is my opinion that the following plants be avoided when considering what to grow in your garden. The numbering is not intended as a scale of invasiveness, but rather arbitrarily assigned.

Purple Loosestrife
Purple loosestrife, Lythrum salicaria, and its cousin, the European wand loosestrife, Lythrum virgatum have both proven to be the worst kind of exotic ornamental weed, taking over thousands of acres of wetland in North America.

1.) European Wand Loosestrife, Lythrum virgatum – this a close relative to purple loosestrife, Lythrum salicaria, the famous invader of wetlands. Nowadays it is illegal to grow L. salicaria throughout much of the USA and Canada, and to date it can be found in all but six states in the USA, and is still spreading in the west. This plant is so invasive that it literally transforms wetlands into near loosestrife monocultures.

The rub is that the very similar European wand loosestrife, Lythrum virgatum, is still sold by many nurseries. Cultivars sold as sterile, safe garden plants have been found to be capable of setting seed if pollinated by other wild growing Lythrum species, including L. salicaria. Germination rates of Lythrum seed is very high, and rampant colonization of wetlands is a constant threat when seed is in the vicinity. Though L. virgatum is reported only from a handful of states in the USA, the truth is that its actual distribution is not well known since it can be easily confused with L. salicaria, and hybrids as well may be much more prevalent that previously thought. To make matters worse, both species are adapted to a wide range of temperatures, growing from USDA cold hardiness zones 3-9 (in other words, capable of living from Florida to southern Canada).

Not surprisingly a number of states have already banned the sale of this species within their borders, including Arizona, Iowa, Montana, Minnesota, North Carolina, North Dakota, Nevada, New Hampshire, Tennessee, Wisconsin as well as Pennsylvania and Washington, where it is already considered a noxious weed. Remarkably, even to this day there are people who grow and advocate growing both species. In my opinion, growing and distributing either is unethical, and should be stopped wherever they are not native. Remaining wetlands have undergone extensive modification or outright destruction in past decades, and combined with increasing human need for water resources, are under tremendous pressure already. Adding to that by growing these highly invasive pests is the coup de grace, and thoroughly inadmissible.

Yellow Flag Iris
The highly invasive yellow flag iris, Iris pseudacorus, a native of Europe and north Africa, has transformed wetlands across North America from central Alaska to Mexico and beyond.

2. Yellow Flag Iris, Iris pseudacorus – another ornamental plant that has literally gone amuck, invading wetlands throughout the USA and adjoining areas of Canada. Currently is it found in all but four states within the US, one being Hawaii. Amazingly even Alaska has populations. Brought in as a garden plant in the 1700s, it has escaped and colonized freshwater as well as brackish water wetlands from central Alaska, thru much of southern Canada, all the US, parts of Mexico and even South America. It rapidly colonizes wetlands forming huge monospecific rafts, out-competing native plants, and can even flourish in shaded swamp forests.

If that weren’t bad enough, it is also toxic, so is a danger to both domestic stock as well as wild animals. Care should be taken when removing it since its sap can cause skin irritation. The seeds have air pockets that allow them to float for months and thus are distributed to new areas. The rhizomes as well break off with age and similarly can be transported by flowing water to colonize other habitats. It is tolerant of a wide range of temperatures, growing from USDA cold hardiness zones 2 thru 10, which is in itself almost unbelievable.

Remarkably, Iris pseudacorus is still sold online, and otherwise traded. Regardless, simply put, this species has no redeeming features beyond its pleasant yellow flowers. If you want to grow an iris, there are many other species and hybrids within the genus that are harmless to the environment and you. Here is another species that should never be grown outside its native range.

Vinca major and minor
The two common periwinkles, Vinca major and Vinca minor, are now rampant pests throughout the USA and parts of southern Canada.

3. Periwinkles, Vinca minor and Vinca major – these lovely little evergreen vining plants complete with pretty lilac blossoms have one major flaw – they are terribly invasive. Brought in as ornamental ground covers as early as the 1700s, both have spread over much of the eastern USA, with V. minor favoring the northern forested eastern and western states, and V. major more frequent in the southeast and Pacific coast states. Though lovely, both are serious invasive pests wherever they are found. Plants that escape from gardens and old homesteads rapidly colonize woodlands, forming dense mats that exclude native species from growing.

This is another one of those, “oh isn’t it lovely and cute” plants (even the name is non-threatening) that is literally more sinister than it seems on the surface. Though the plants are rather short and seem innocuous, their root systems are extremely vigorous and penetrate several feet into the ground, out-competing other plants and thus creating sterile monocultures. In southern Indiana for example there are many hundreds of acres of these periwinkle monocultures dominating forest floors there.

Natives of Europe and the Mediterranean region, they need to remain where they are found naturally. Even here in southern Japan I see them escaped into the local forests. Remarkably, to this day both are commonly traded and sold, and as far as I know, not legally controlled by any state in the USA. Another plant to avoid regardless of legality in my book.

Japanese climbing fern
The Japanese climbing fern, Lygodium japonicum, is not only fascinating, but also an aggressive weed in southeastern US forests and wetlands.

4. Japanese climbing fern, Lygodium japonicum – this odd little Asian fern is a true vine, growing high into the forest canopy when happy, and is cousin to Lygodium microphyllum, which has become a menace to the wetlands of central and south Florida. Though relatively not well known, L. japonicum is established in much of the southeastern USA, particularly in Alabama, Florida, Georgia, Louisiana, Mississippi, South Carolina and eastern Texas where it rapidly colonizes disturbed sites and plantation forests.

It frequently grows from the ground up into the canopy (to 30 meters, or 90 feet) forming a “petticoat” up the tree, and in fire events this can aid in setting crown fires which destroy trees outright, but have little effect on the fern since it rapidly regrows. In Florida this fern is establishing in native habitats as well, particularly wetlands, and seems to be increasing in distribution, apparently from north to south. It has also been found in remote regions of the Everglades and Big Cypress Swamp, so it is effectively moving on its own.

Brought in sometime around the turn of the last century, this plant is now firmly established in many southeastern states. While its relative L. microphyllum is now illegal to import or distribute in the USA without a permit, this species is not regulated as yet. Given it is more capable of handling cold, surviving up to at least USDA cold hardiness zone 7, it seems it could become an even greater threat than its cousin to southeastern wetlands and forests. For this reason I highly recommend avoid growing this species either in the open garden or under glass.

Coral Ardisia
The coral ardisia, Ardisia crenata, is a gorgeous evergreen shrub of south Asia. In the last 40 years it has escaped cultivation in the US gulf states, invading forest ecosystems, especially in Florida and Texas. Here it is growing in its native Japan, where it poses no threat due to natural limiting factors on its growth.

5. Coral Ardisia, Ardisia crenata – here’s another lovely plant that at face value looks like a winner for southern gardens, and so it seemed for many years. This plant was first introduced into Florida about a hundred years ago and seemed to be just another beautiful shrub with its broad evergreen leaves and copious umbels of brilliant red berries. Then in the 1980s folks started to notice it was finding its way into nearby woodlands. At first it seemed to be restricted to Florida, but then infestations were reported in eastern Texas, and more recently in Louisiana, Alabama, and even Hawaii.

The problem with this plant stems from its red berries, that while lovely, are produced in vast quantities and have very high germination rates. A single adult plant that has escaped into a native woodland can have a literal carpet of seedlings around its base. In time these grow into adults and before you know it, you have a vast grove of A. crenata dominating the forest floor. This species is a native of dark forest floors, needing little light to thrive, and easily crowds out native herbs, grasses and ferns. Populations are now well established in both urban areas as well as native forests, and it is probably still expanding its range outside of Florida.

Currently coral ardisia is illegal to possess, sell or transport within the state of Florida where it is now widespread. In other southern states it remains a growing threat. Though its advance northward will be thwarted by cold winter temperatures, it is likely it will be able to spread into much of the warmer parts of the southeast, certainly to USDA cold hardiness zone 8, and even perhaps the warmer parts of zone 7. Given its high invasiveness, here’s another one to avoid in the garden even outside of Florida.

Flowering Mimosa Tree
The mimosa tree, Albizia julibrissin, has such elegant flowers and foliage that it is nearly irresistible to exotic gardeners around the world, and yet it has proven to be a highly invasive species outside its native homelands.

6. Mimosa tree, Albizia julibrissin – this lovely tree with its pink pom-pom shaped flowers and soft, fern like foliage has earned it many colorful names such as silk tree, silky acacia and powderpuff tree. Originally a native of southern Asia, it was introduced into the USA in the mid 1700’s and has firmly established itself throughout the southeastern states, mid-Atlantic region, Ohio River valley, and parts of the west as well.

It’s elegant tiered branching and soft pink flowers beguile, but beware, this tree is highly invasive. An opportunist, it quickly dominates disturbed land such as fallow fields and roadsides in particular, but is highly adaptable to different conditions, often favoring natural waterways. It is fast growing (up to a meter a year), quickly resprouts if mechanically damaged (including severe pruning, frost damage and fire), and produces abundant seed that can remain viable for decades. It can quickly form dense thickets that blocks out sunlight for other plants. Trees growing along rivers and streams pose a greater threat since the seeds are easy spread downstream.

To this day the mimosa tree is grown as an ornamental tree throughout the world. There are even deep purple-red leaf cultivars that are nearly irresistible to exotic garden hobbyists. In the southeastern US it is considered a weed species and is being closely monitored and controlled. In Tennessee it is considered a severe threat, while in Georgia it is on the top ten most invasive plants, and a weed capable of altering plant communities in Florida. In other areas is listed as moderately invasive, but this could change with time. Though largely unregulated, this remains a tree that should not be grown outside of its native lands in my opinion.

Chinese Tallow Tree
The Chinese tallow tree, Triadica sebifera, is a sight to behold in fall, easily rivaling native maple trees. It also has become an invasive weed throughout the southeastern USA where it is taking over wetlands of all types, from freshwater prairies in Florida to salt water marshes in South Carolina.

7. Chinese Tallow Tree, Triadica sebifera – another angel in disguise, this native of China and Japan is now a rampant weed in subtropical regions around the world. It was brought into the Charleston, South Carolina area in the 1700s since the coating of its seeds can be made into wax, soap, and even fuel. For years it was allowed to grow unchecked, and current now populations exist throughout the southeastern USA from coastal North Carolina to central Texas. More worrisome are  reports of disjunct populations in northern Tennessee, Kentucky, California, and even southern Wisconsin, indicating that its spread may not yet be full realized. In California it is a relative newcomer, with populations along river systems still on the increase. In Florida it is now almost widespread, with just a handful of counties still free of the pest.

This is one adaptive plant, capable of producing flowers in the first year of growth, and adult trees are estimated to produce 100,000 seeds each year. While the plant seems to thrive in riparian zones (wetlands along rivers and streams), it also happily invades marshlands. Here it isn’t fussy either, growing in fresh, brackish, or salt water marsh. If that weren’t enough it can grow on fallow land, in both full sun or deep shade. Very quickly infested lands can become vast monocultures of this tree, replacing other trees, grassland species, and even effecting reproduction of frogs. Moreover, while the seeds are dispersed by hungry birds, both leaves and seeds are poisonous to livestock and humans, causing skin irritation and if eaten, vomiting and diarrhea.

Amazingly, this tree was sold until very recently as an ornamental since it can grow in almost any soil, is drought tolerant, fast growing and has lovely red to orange fall foliage. It now is classified as a noxious weed through the gulf states, and efforts are under way to control it wherever it is found in abundance. This one is another unsuitable plant for any garden, and existing trees should be removed ASAP.

Asian Privet Bushes
Privets, genus Ligustrum, are Asian evergreen bushes first brought to the USA to form hedgerows, but now have escape cultivation, invading fields, forests and wetlands across the country.

8. Asian Privet, Ligustrum species – this group of Asian evergreens, capable of growing to small tree proportions, are represented by the following species in the USA: L. lucidum, L. japonicum (pictured above), L. ovalifolium and L. sinense. Of these, L. sinense is the most widely distributed, occurring even into the lower Midwest and southern New England states, while L. lucidum and L. japonicum are found largely in the southeast, particularly Florida and the gulf states, with outlying populations in California. L. ovalifolium is far more widespread, but with much less impact (so far) than its relatives.

Privets were brought into the USA around the 1800s as ornamental shrubs and for making hedgerows. In early summer they produce large heads of white flowers, and in the fall bunches of black-purple berries which are readily eaten by wildlife and dispersed. Plants can spread from root sprouts as well, thus forming dense thickets that crowd out native species, particularly low growing herbs and grasses, and to a lesser extent sprouting tree seedlings. They can invade all manner of habitats, from open fields to closed canopy forests, and even wetlands.

Although Florida lists L. sinense as a noxious weed, these bushes remain largely unregulated in the USA, and though they are being closely watched, there are no federal controls on growing and distributing them. Here’s another group of plants that are just too invasive to be good candidates for the garden.

Mexican Petunia
The Mexican petunia, Ruellia simplex, has become another noxious pest in the southern USA, especially in peninsular Florida where it is now virtually widespread.

9. Mexican Petunia, Ruellia simplex – here’s another would be innocuous herbaceous perennial for southern gardens that has turned into a nightmare plant. A native of Mexico and South America, it was introduced into Florida sometime in the 1940’s. This vigorous weed now is found in throughout peninsular Florida as well as parts of South Carolina, Georgia, Alabama, Mississippi, Louisiana and Texas, as well as Hawaii, Puerto Rico, and the US Virgin Islands. It has also become a pest in eastern Australia, and to some extent, Japan as well.

Mexican petunia readily invades wetland communities in particular, including marsh/prairie habitats as well as more shaded forested swamp lands. It has been found that even after being killed back by herbicidal treatments, this plant quickly recolonizes, crowding out native species. Not surprisingly, it can withstand a wide range of environments, the seed has high germination rates and plants quickly recover if cut down, burned, etc. Simply put, it has all the characteristics of an invasive weed.

Ruellia simplex is now considered a noxious weed in Florida, capable of altering native plant associations. Though its range is spotty north of peninsular Florida, it is cold hardy to at least USDA cold hardiness zone 8, making its expansion northward just a matter of time. Efforts have been made to breed sterile forms for the outdoor garden, but honestly I personally do not believe they should be trusted. There are just too many safer choices for the garden, both exotic or native, so why take a risk with this invasive time-bomb?

Spanish Bluebells
The Spanish bluebell, Hyacinthoides hispanica, is another invasive pest in western Europe and parts of Canada. Its lovely blue, pink and white flowers belie its real character – a rampant weed.

10. Spanish Bluebells, Hyacinthoides hispanica – what could be more wonderful than a vast field full of bluebells in the spring? Answer – some other plant that doesn’t take over everything. Although this species is not yet considered a serious problem in the USA or Canada, it is a problem in western Europe where it is hybridizing with native bluebell species (H. non-scripta) to produce the invasive, fertile hybrid H. x massartiana. In Vancouver, B.C., Canada, all three of these bluebells exist, and like in the UK and Ireland, they are causing concern, but as yet are not considered seriously invasive. Although a beautiful plant, all parts are toxic to humans and animals.

That said, this bulb forming plant originally native the Iberian Peninsula and north Africa has been found to be very unruly in the garden. Its bulbs easily multiply and are deeply rooted, making them difficult to fully dig up and remove. Anyone who has seen them take over, often in fairly shaded woodlands, can attest to their ability to dominate. I have seen them growing on Salt Spring Island, B.C., Canada in a native woodland (admittedly along a road), thus proving their ability to expand into native plant communities. Add to that, this species can thrive in a wide range of temperatures, from USDA cold hardiness zones 3-8, making its potential spread truly frightening.

As yet completely unregulated in the USA or Canada, H. hispanica, H. non-scripta, and their hybrid, H. x massartiana, are in fact still openly sold and traded as safe, reliable garden plants. Again, given the danger to native ecosystems, and the potential for becoming yet another prolific garden weed, why consider growing this plant?

So there they are, ten species of exotic ornamental plant you’d never find in my garden. Lovely, perhaps, but at what cost? Ethical concerns aside, we are unfortunately already experiencing the effects of their presence, and the real question now is how can we stem the tide in the decades to come? One answer that is simple is to just not grow any of them. That’s my ten cents.

Ume, the Japanese Plum Tree, Prunus mume

The Japanese plum tree, also known as ume, Prunus mume, is in fact an apricot, and originates not from Japan, but rather the mountains of southwestern China. Regardless, this is another iconic tree of Japan, famous not only for its early flowering, often while the snow still falls, but also for its extremely sour fruits which are used liberally in Japanese cuisine – from pickles to sauces, and also as a spice.

This flowering tree is a member of the Armeniaca section of the rather large genus Prunus, which includes cherries, peaches, plums, almonds, and apricots. This last group of fruit trees, the apricots, are best known by the species Prunus armeniaca, the source of the common edible apricot that has been in cultivation for thousands of years. The seven other members of this group are rather obscure with the exception of P. mume, which has been in cultivation in China for over a thousand years, and probably a least a thousand in Japan as well.

Prunus mume in full flower
Prunus mume in full flower in February, Maizuru Koen, Fukuoka, Japan, February 2006.

Prunus mume is a relatively small tree, ranging from 4 to 10 meters in height if left unpruned. It’s flaking bark is typically gray when mature, and with a green tint and smooth when young. Branching is complex and fine. It is a deciduous tree, bearing lanceolate to obovate leaves, typically finely haired, with toothed margins and usually not more than 8 cm in length. Trees are not terribly long lived, perhaps up to a hundred years. The flowers are born singly or at most doubly per fascicle, and open before the leaves by several weeks. Since they flower during cold weather, they can last quite long, up to two weeks or more, before falling.

In simple flowers, the petals are 5 in number, ovate, and about 1 cm long. Multi-petaled types can have many petals and be double that size. Flower color originally was typically white with a pink blush, but nowadays ranges from deep crimson to various shades of pink, pure white, and even green blushed flowers. Depending on latitude and elevation, flowering typically commences from late January into early April, but always well before most trees have begun to break dormancy. The fleshy fruits, known as drupes, range from 2 to 5 cm in diameter, maturing a deep yellow with red-purple blush, and are fully ripe by middle June in Japan.

Prunus mume simple flower
Simple flower varieties of Prunus mume have 5 petals. This white flowered form is closer to the ancestral type.

The precise origins of this species are somewhat unclear given its long history of cultivation, however the likely center of its natural range was where the Yangtze River breaks into its three main constituent sources – the Min, Quingyi, and Dadu Rivers in western Sichuan, near the city of Leshan. It is said to be native to both northern Yunnan and western Sichuan Provinces in forested mountains ranging from 1700 to 3100 meters elevation. That said, it is widely cultivated throughout China, as well as northern Laos, northern Vietnam, Taiwan, Korea as well as Japan. Increasingly, it is is becoming more widely cultivated in Europe and North America in recent decades.

Prunus mume has been selected and cultivated over hundreds of years, and in some cases crossed with similar species, to produce an astounding array of named varieties. In Japan alone, over 500 types have been created, making classification complex and often obscure. Regardless, in Japan most fall within three main groups. They are as follows:

Yabai (野梅系) – These types are the closest to the wild type. Branching tends to be thin and dense, with the smaller branches being somewhat thorny. Flower color typically is white, with pink blushing, particularly on the tips of the buds and inner petals. The leaves are more lanceolate in shape, and are covered in soft, fine hairs.

Hibai (緋梅) – This group includes the forms known as Koubai (紅梅), characterized by their deeply red colored flowers. While these forms tend to produce many smaller flowers that are red in color, some can be white or pink. They are said to be derived from the Yabai group. The pith of the inner wood as well is red in color, as are the the leaf petioles. The leaves are small in size, and similar to the Yabai types. These are commonly grown as garden trees and as bonsai, and less so for their fruit.

Red flowered form of Prunus mume
The deep red flowered forms are known as Hibai or Koubai, and typically grown for their colorful flowers rather than their fruit.

Bungo (豊後) – This group was developed in the historical province of Bungo in present day Kyushu in Oita Prefecture. They are apparently crosses with the closely related P. armeniaca, known as anzu in Japan. Being hybrids, many are not self compatible and have to be out-crossed to create viable offspring. They are said to have low disease resistance, but ironically are also more cold hardy, presumably due to the influence of the colder growing P. armeniaca. For that reason they can be grown even into the Tohoku Region of northern Japan. Flower color and form is variable, from red to white, boasting both single to multi-petaled types, and tend to be later flowering. Branching is relatively thick and sparse. The leaves are usually more ovate than pure P. mume, and hairless. Unfortunately, the fruits tend to have rather fibrous pulp, and for that reason they are not favored for use in cuisine.

With those distinctions aside, there are other characteristics that define the many varieties of this tree. These include: type of branching, flower color, flower size, flower complexity, fruit size and texture, wood color, bud color, flower stance, and so on. Needless to say, differentiations are complex, and as with many things in Japan, subtle. What follows are a few broader examples of this complexity.

Ume flowers in the snow
Ume trees flower in mid to late winter before snow stops falling. Both the buds and flowers of this tree are resistant to moderate frost.

Simple flower types – these can be any color, from red to white, but are consistently 5 petaled, and are closer in form to ancestral types.

Multi-petaled types (called yayae in Japan) – these have thicker looking flowers, with varying numbers of petals depending on the variety. Again, flowers can be various colors, and tend to be rather large in size, commonly twice the size of many simple flower varieties.

Large vs. smaller flower types – flower size can vary considerably regardless of flower complexity. Some, particularly the deep red varieties, can have almost tiny flowers (~1 cm across) while some of the larger ones can approach 6 cm in diameter.

Weeping branched types (called shidare in Japan) – like the weeping cherry trees, one can see lovely examples of weeping ume too. Most commonly the flowers are pink and also multi-petaled. White flowered forms are more uncommon.

Green Flowered types (midorihana) – yes, breeders even have managed to produce flowers with distinctly green tinted blossoms.

Early and late flowering types – some varieties have been selected and bred to flower as early as December, others as late as early April (these are Japan flowering times).

Weeping Prunus mume tree
The weeping branched form of Prunus mume is known as shidare form in Japan.

The subtle variations between size, flower form, color and so on seem almost limitless – enough to intrigue you for a life time, or drive you stark raving mad (or perhaps bored). Trying to keep track of the names of each variety, its characteristics and province is literally a field of study within itself.

The scope of influence this tree has had on Japanese culture is equally impressive. During the Nara Period the plum flower was adopted as a crest (umemon) by several prominent Japanese families, including samurai. Famously, this tree and flower was beloved by Michizane Sugawara of Dazaifu Tenmangu shrine in Kyushu – a politician, scholar, and poet of the Heian Period. To this day his beloved trees adorn the grounds of the shrine, and thousands of students visit annually to get his blessing, since he is to this day worshiped as a god of learning.

The fruits of this tree remain a significant part of the Japanese diet. They are commonly consumed in a salted, pickled form known as umeboshi. These pickles are somewhat of a surprise to the uninitiated, being that they are at once sour in the extreme, as well as very salty. I have watched more than one foreigner choke one up. They are best eaten as a topping for white rice or in a rice ball (onigiri). Eating them as is takes some practice. Pickled ume fruit can have various levels of sweetness, from quite sweet to purely sour, as well as in texture, from crunchy to sticky soft, and even as a slightly moist, candy-like snack.

Beyond pickling them, ume fruit are used to make ume plum vinegar (commonly taken as a health drink), umeshu (a strong liquor made by soaking the unripe fruits in white liquor for months or even years), and also as a flavoring for almost any dish including crackers, candies, dressings and even seaweed.

The flying ume tree
This famous three trunk ume tree at Dazaifu Tenmangu is called tobiume, meaning “flying ume”. The scholar and politician Michizane Suguwara was banished from his position in Kyoto society to the backwaters of Kyushu during the Heian Period. It is said these beloved ume flew from Kyoto to Kyushu to be with him, Dazaifu Tenmangu Shrine, Kyushu, Japan.

The driving force behind all this ume fruit consumption is not only the pleasant sour taste, but the presumed health benefits they are said to have on the human body. The sourness of the fruit belies the presence of a healthy dose of ascorbic acid, common known as vitamin C. They are so acidic that they are literally impossible to eat as is, even if fully ripe, soft and yellow. For that reason they must be processed in some way to mediate their extreme sourness.

Ironically, while eaten as a health food, the unripe fruit also contain toxins that if consumed in large quantities can kill. These poisons are glycosides of hydrocyanic acid, amygdalin and prunasin, commonly found in many Prunus tree leaves and seeds, including common fruit trees such as peaches, plums and apricots. Consumption of these glycosides and the subsequent interaction with gastric acid in the stomach can cause the production of hydrogen cyanide which ultimately leads to convulsions, shortness of breath, paralysis, and eventual death to those who eat too much.

But here’s the rub – the danger rests only with over-consumption of the seeds (which amazingly ARE still eaten by some stubborn people). Moreover, the processing of the fruits, whether unripe or ripe, through the use of alcohol, salt and sun drying, inactivates the enzymes necessary to produce cyanide, hence toxicity levels drop to a minimum. Believe me, eating potato chips is far more dangerous to your health than eating ume based products! All that said, care has to be taken since umeboshi can contain up to 10-20% salt content per weight.

Far from being a dangerous food, thousands of years of eating these fruits in the far east has confirmed that they are not only safe to eat, but also harbor medicinal effects. The known health benefits of vitamin C aside, P. mume fruit have been used in China medicinally for centuries to aid in stomach and intestinal ailments, in controlling intestinal parasites, preventing bleeding (hemostasis), and in suppressing both gram-positive and gram-negative bacteria, as well as pathogenic fungi in vitro. Research in Japan has also indicated that consumption of ume fruit reduces fatigue, increases HDL cholesterol significantly, decrease the chances of developing arteriosclerosis, decreases blood pressure, and stabilizes blood sugar levels.

Unripe ume fruit
The unripe fruits of Prunus mume are a rich source of vitamin C, but are so sour they cannot be eaten as is. They also contain cyanoglycosides that need to be neutralized before consumption.

My own experience with this tree started when I moved into my house in southern Japan 15 years ago. Next to the carport was a well aged, overgrown Prunus mume, though I didn’t know it was that species at the time. In time I found out what it was and realized it had to be pruned soon or it was going to overtake the yard the following season. So, with little knowledge, I hard pruned it soon after it flowered, sometime in mid April. Much to my surprise, it responded by shooting out hundreds of meter long whip-like shoots a month later. Not sure what to do, I in response pruned these back by half.

I learned the hard way that if you want to keep your ume tree to a contained size, it is important to not only know how, but when to prune. I learned that it is best to prune after the fruits have fully matured, that being around late June to early July in my area. If you prune at this time, the tree will not respond by sending up lots of vigorous shoots, but will rather harden off and heal the cut shoots, and then put resources into forming new flower buds on the remaining green wood. This last bit is important when pruning them since cutting back to the older, hardened wood leads not only to completely defoliating the tree (and it subsequently suckering like crazy), but it also prevents the tree from flowering the following season.

For trees that are being pruned to small size, new shoots will begin growing a few weeks after flowering is finished. These normally range from 20-40 cm in length, and start hardening off by the time the fruits are ripening. I usually leave 2-4 buds on each pruned shoot, thus allowing new flower buds to form for next year, as well as containing the overall growth of the tree. In addition, since these trees will produce many new shoots off old wood, it is necessary to routinely remove these to prevent dense branching from forming. P. mume can produce many fruits and this can lead to branches breaking in the wind if shoot length and density is not managed properly.

Here’s a video showing these trees in southern Japan:

For those interested in growing this tree primarily for fruit production, I suggest following methods used to prune other similar trees. In Japan fruit producing trees are typically grown rather flat by constantly cutting out the central lead growth, and encouraging lateral branching. This allows for easier picking since if left unpruned these trees can get quite tall. Again, branch density as well has to be controlled, since heavy fruiting will lead to lower quality and sized fruit.

Regardless, unless you are willing to allow these trees to grow to normal proportions, yearly pruning will be necessary to either keep them smaller, or to optimize fruit production. Luckily, this tree is very responsive to annual pruning, and as stated before, is commonly trained as bonsai.

Interestingly, there is one exception to the pruning technique outline above, that being how to prune the weeping forms. It is common to hard prune weeping ume trees directly after flowering to the old wood, thus causing the tree to sprout many long suckers which naturally hang downward in almost an inverted umbrella shape. This type of pruning leads to massive displays of weeping branches covered in thousands of flowers the following year.

Ripe ume fruit
Ripe ume fruit look very much like typical apricots, but even though full of sugar still are too sour to consume.

Beyond pruning, cultivation is fairly straightforward. Trees should be sited in full sun, preferably in a well drained loam with a moderately acidic reaction. Established trees can endure some drought, but will suffer if not watered. I have found fertilizing unnecessary in the native soils of Japan, but in low nutrient soils, particularly deep sands, you may need to feed them. This is best done in the spring, and perhaps again in summer.

The greatest limitation of this tree is its cold tolerance, which is fairly low. It can be grown reliably in USDA cold hardiness zones 8, 7 and perhaps the warmest parts of zone 6. In colder winter regions it should be sited well, offering as much protection as possible from winter winds in particular. A south facing wall or courtyard may be the best choice in these places. Since flowering starts so early, the risk of it being affected by late cold snaps is another issue, though the flowers and flower buds are able to endure moderate frosts.

Disease issues are fairly minimal, and mostly involve the young tender leaves and shoots. Each year my tree gets infestations of aphids, and at times these can get quite intense, though short lived. If there is a severe outbreak I spray effected branches with strong jets of soapy water which usually seems to do the trick. Since aphids can also spread disease, mass infestations can lead to sooty molds growing on the effected branches as well. I have seen outbreaks of both simultaneously on trees in Japan, and though this rarely hurts them in the long-term, it can effect the growth and health of the developing fruits.

Another common issue with older trees is heart rot. This does not usually kill the tree outright, but it can weaken it significantly, causing the tree to become less stable. Assuming an effected tree is otherwise fairly healthy, it can live with heart rot for many years. The best way to avoid the development of this problem (which is a fungal rot of the inner wood) is maintaining good cultivation practices such as not over pruning trees, not injuring the bark, and otherwise providing good growing conditions – plenty of sun, not overcrowding the tree with other vegetation, and providing healthy levels of nutrients and moisture to the roots.

If you live in a warm temperate climate, or have a protected place in the garden, you might want to try growing Prunus mume yourself. It’s lovely little flowers blooming far in advance of most garden plants are a respite from winter’s cold, and serve as a welcoming harbinger of the spring to come.

Fairy Slipper Orchid, Calypso bulbosa

The cold woodlands of the northern hemisphere are the dwelling place of a tiny, delicate orchid, Calypso bulbosa, aptly named after the Greek nymph. When you first see it in person you are immediately taken back by its seductive beauty and elusive stature. This diminutive plant, also known as the fairy slipper, can be found from cold temperate regions across the northern US, up through the boreal forests of Canada and Alaska, straight across the taiga of Russia, into Scandinavia, and south through the mountains of western China, Korea and northern Japan. It is nowhere truly common, and is often overlooked.

C. bulbosa, as the name indicates, grows from a single oval subterranean bulb no bigger than the average fingernail. In the winter months a single broad, lightly pleated leaf arises just above the forest floor, only to wither in the summer months during the plant’s dormancy. It regrows again in the fall, just before the snows of winter hit. The flower stalk, occasionally up to 15 cm tall, but often much shorter, begins growth once the cold of winter has abated. Depending on exposure, as well as altitude and latitude, plants are in flower from April to June. The flowers are borne singly at the apex of the flower stalk, and are accompanied by a whitish, translucent floral bract at the pinnacle of the stalk.

fairy-slipper adult plant
Adult plants of Calypso bulbuosa typically are no more than hand high.

Despite being quite small, the flowers are startlingly beautiful, though you’ll have to get on your belly to really appreciate them. Five of the flower parts are nearly identical in size and shape, two petals and three sepals, splayed out in a star-like pattern. The lip is slipper-like, similar to a lady slipper (genus Cypripedium), but more elongated with a frilled front plate with upward curling margins. At the front of the mouth of the lip are a number of hairy bristles. At the base of the lip, sometimes extending a fairly long distance beyond the lip proper (especially in v. speciosa) are two horn-like projections. Overall flower color is pink-purple. The column is held horizontal to the ground, is relatively long and has a broad hood.

The lip is striated with white and various shades of darker purple, or purple brown veins and spots. Variety americana is known for a bright yellow patch in around the area where the bristles protrude, making it perhaps the most attractive of the four known varieties. Pure white alba flowers, as well as pale “semi-alba” types are also known. Occasionally, two flowers can be found on one stalk. Seed pods develop in an upward standing position.

Calypso bulbosa flowers
A pair of Calypso bulbosa v. occidentalis growing in a coniferous forest in East Sooke Park, Vancouver Island, Canada.

There are currently four accepted varieties of C. bulbosa:

C. bulbosa v. bulbosa – a denizen of northern Eurasia from Scandinavia and extending across the boreal forest regions of Russia to the Korean Peninsula and northern Japan. This was the first variety to be described by the father of binomial nomenclature, Linnaeus, in 1753.

C. bulbosa v. speciosa – confined to the high mountains of western China, parts of inner Mongolia and central Japan (limited to high elevations of the Southern Japanese Alps; Yamanashi, Nagano, Shizuoka, and Saitama Prefectures). Somewhat of an enigma, it is not completely certain that Chinese and Japanese plants are of the same type. In China and Japan it is found in subalpine coniferous forest up to 3,200 m (~10,500’) elevation.

C. bulbosa v. americana – found across the entire boreal region of North America from the Atlantic to Pacific, as well as the mountainous regions of the western US (in Canada it is widespread in forested regions, in the US from northern Maine, Vermont, Michigan, Wisconsin, Minnesota, South Dakota (Black Hills), Montana, Idaho, Wyoming, Washington, Utah, Colorado, New Mexico, Arizona, Alaska; historically N.Y. (last seen in 1969) and New Hampshire. Known for growing into large, clumping colonies and having yellow crested lips. Largely restricted to northern white cedar (Thuja occidentalis) and balsam fir (Abies balsamea) swamps east of the Mississippi River, but occasionally found on drier sites in mixed coniferous/deciduous forest often over limestone bedrock. In Michigan it can be found in swales between old lakeside dunes in jack pine forest (Pinus banksiana) alongside Cypripedium arietinum. In the western US it is found at mid-elevation coniferous forest in the northern Rocky Mountains, and up to 3,000 m (10,000’) in Arizona, its southernmost distribution. In Canada it is found from Labrador to British Columbia, and northward to the Northwest Territories, typically in coniferous forest.

C. bulbosa v. occidentalis – confined to western North America from California to Oregon, Washington, Idaho, Montana, British Columbia, and Alaska. In the south it is found exclusively in cool, “fog-belt” coastal forests, and further north (Idaho and Montana and northward) it can be seen in moister inland mid-elevation mountains as well. It is a characteristic plant of the Pacific Northwest rain forest belt often seen near sea level, and flowering earlier than most other varieties.

Calypso bulbosa leaves flower buds
The leaves of Calypso bulbosa grow in the fall, persist through the winter months and go dormant after flowering in the spring. In this photo you can also see the flower buds have formed and they too overwinter, so care must be taken to protect these if you are growing the plant.

My first encounter with this species was in the high mountains of Colorado near Rocky Mountain National Park. I was there in the early fall and so did not see them in flower, but their distinctive leaves gave them away. Years later I saw large colonies in the mountains around Bozeman, Montana, again in the fall. It wasn’t until I finally made a trip to the Victoria, British Columbia area in May 2019 that I finally got to see v. occidentalis in flower, growing in Douglas fir (Pseudotsuga menziesii) and western red cedar forest (Thuja plicata) just above the pounding waves of the Salish Sea. It was a magical experience for me, and upon seeing them I was immediately convinced that both Calypso and fairy slipper are very apt names for this little jewel.

Calypso bulbosa, though widely distributed, is becoming increasingly rare, particularly in the southern end of its range. It is considered rare in the lower 48 states except in a handful of states, and in the northeast it is either vulnerable, endangered or extinct. Populations in Minnesota as well as the northern Rockies and Pacific coast appear secure for now, and likely Canadian populations are by and large in pretty good shape, too. In Japan plants are in danger due to climate change since populations are confined to high mountain forests that are undergoing rapid warming. Populations in Europe are considered near threatened by the IUCN (International Union for Conservation of Nature). In all regions where urbanization is occurring (for instance around Victoria, B.C.) populations are being adversely effected by development and increased human disturbance. In various places it is also subject to over collection for the horticultural trade, for example, in the Japanese Southern Alps and the Pacific Northwest of North America.

Calypso bulbosa alba flower
All varieties of Calypso bulbosa have individuals that are either true pure white “alba” flowers, or very pale ones like this “semi-alba” flower.

First and foremost, this is a plant of cool to cold forests, hence if you want to grow it, you need to keep this in mind. It likely will not endure temperatures above 26 C (80 F) for long periods of time. The main reason it lives either at high altitude or in cedar bogs at the southern end of its range is due to the cool conditions these environments provide. Another important point is that this species does not live in soil, but rather in the thin layer of humus overlaying forest soils, or moss covered humus of bog environments. Third, this orchid appears to have a dependency on mycorrhizal fungi even throughout adulthood. For all these reasons it will be a challenge to maintain in most typical garden settings, particularly in areas that experience heat spells for more than say a few days.

Another issue in growing them is their diminutive size. They can be harmed by foot traffic, either human or animal made, very easily either through mechanical damage or the compacting of the growing medium. Snails and slugs are another bane of this plant, and unless diligently controlled, will be the end of them in short order. Rodents as well need to be kept away. Mice, voles, pika, marmots, rats and the like can make an easy snack out of a Calypso in just a few bites. Likewise, moles and burrowing animals need to be controlled lest the thin roots and tiny bulbs are damaged or exposed to the air. Finally, these plants are so small that they cannot endure much competition from neighboring plants including grasses, any type of ground cover, spreading bushes, or indeed even vigorously growing mosses.

If all that weren’t enough, something like 99.9% of the plants that you might find for sale are for certain wild collected. While that may not actually be a legal issue, and in truth this species is considered globally secure for the time being, it may give you an ethical pause. In this world of online auctions and on demand next day delivery, one can easily see that all collectable plants are more at risk than ever before. Yes, this species has been produced artificially, but only by a handful of knowledgeable enthusiasts, and certainly not on a commercial scale. So, as with all terrestrial orchid sales, buyer beware.

With all that in mind, if you still desire to grow C. bulbosa, and have access to healthy plants and proper fungal symbionts (best acquired by getting humus or conifer duff from a known habitat), then you may succeed with this species. It should be grown in shady conditions, never in direct sun. The compost needs to remain moist during the growth phase extending from fall until late spring. In summer some drying is tolerated, but droughty conditions are not recommended. Never use chlorinated water or high mineral water or you will kill them quick. Keep the growing compost cool at all times, even if the air temperatures exceed the mid 20s C (above 80 F). A northern exposure is recommended rather than southern to prevent overheating.

Grow the plants in a thin layer of partially decomposed conifer duff no more than 5 cm (2”) deep over a continuously moist layer of neutral to slightly acidic inorganic material such as river sand, perlite, Turface, small size pumice or the like. The point is that you don’t want this layer to modify the conifer duff layer chemically or mechanically, say from earthworms or soil burrowing insects. Companion plants need to be completely noncompetitive or absent altogether. A layer of moss is OK as long as it doesn’t overgrow the orchids (that’s one way they are overwhelmed even in the wild), and in fact the plants will do better by themselves. If you have a native forest, or forest-like condition in the outside garden, and you live near natural populations, you may try this one in the open garden. Otherwise I recommend growing them in containers and keeping these well protected throughout the season in an outdoor shade house or the like. Refrain from using fertilizer of any kind, even at weak dilution rates.

Calypso bulbosa flowers in nature
A group of Calypso bulbosa v. occidentalis in their full glory, East Sooke Park, Vancouver Island, British Columbia, Canada.

So, there you have it: a tiny little jewel of a plant better suited to being appreciated in nature than in a garden setting. Let’s hope this lovely little orchid continues to grace the far flung woods of the north county for many years to come.

The staghorn fern, Platycerium bifurcatum, a cold hardy subtropical fern

Platycerium bifurcatum, commonly known as the staghorn fern or elkhorn fern, is a modestly cold hardy subtropical epiphyte native to eastern Australia and parts of the the East Indies. Though no species of the genus Platycerium can be called truly cold hardy, this species is capable of handling temperatures down to 27 F (-3 C) with minimal damage. This article chronicles a plant I’ve grown in my yard in southern Japan for the last 11 years – a climate that has tested the boundary of its cold resistance many times.

P. bifurcatum is without a doubt the most commonly propagated member of this relatively small genus of epiphytic ferns (~18 known species). Like many ferns, these grow two types of fronds, fertile and infertile. The fertile fronds are elongate, leaf-like and bear spores, while the infertile fronds (also called shield fronds because of their flat, spreading habit) have no spores. In P. bifurcatum the fertile fronds are forked (bifurcate), looking like a deer’s antlers. The shield fronds grow more or less flat against whatever they are mounted on, and are roughly circular in shape. In time plants can form formidable clumps, spreading by “pups”, or offshoots that grow off small stems (called rhizomes), just below the shield fronds. Large clumps can grow to nearly the size of a small car!

Platycerium bifurcatum
Platycerium bifurcatum growing my garden in southern Japan, on the island of Kyushu.

P. bifurcatum is the most commonly available cold hardy staghorn fern. Only one other species is perhaps even more cold hardy, that being P. veitchii, which is said to handle 25 F (-4 C) without suffering. P. bifurcatum is reliably cold hardy down to 27 F provided that any given frost event is not terribly long, and the following summer is long and warm enough to allow it to recover fully. It can even take down to 24 F (-4.5 C), but events like this must be very sporadic, or the plant will not be able to recover.

I moved to my current house in the fall of 2004. It is situated on the edge of some moderately tall mountains (up to 3000 ft, or 900 m elevation), and is approximately 3 miles (~5 km) from the sea. The region rarely sees below 27 F, but can get down to 23 F (-5 C) on occasion. Winters are relatively short, starting in earnest by mid to late December, and finishing by late February. During this time frosts are frequent, but usually last no more than a day. Average temperatures during this period normally are 43-45 F (6-7 C) overall, with highs around 48 F (9 C) and lows just above freezing. Winter rain is frequent, but usually light to moderate. Snow is also common, but short lived, normally melting within a few hours of accumulating.

By contrast, both spring and fall are long and mild. The frost free months extend from early April through late November or early December. Spring is followed by a strong summer monsoon, lasting from early June to late July. Temperatures during this period are warm, averaging around 77 F (25 C), and most days are cloudy with at least some rain. From late July through mid September is the real heat, with daily highs averaging between 90-93 F (32-34 C), and lows only down to 79-83 F (26-28 C). This is a time of true tropical heat.

I mention all of this to give a context for describing how P. bifurcatum has performed in my garden over the last decade. Based on my results, you can get an idea of whether your climate will be suitable to try this one outdoors or not. I will add that my plant has received no special winter protection, not even from snow. So lets see how it has progressed through the years, and what setbacks it has also endured.
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Cultivating Paphiopedilum armeniacum, the cold hardy Chinese yellow slipper orchid

In the summer of 2013 I bought a nice flowering division of the cold hardy Chinese slipper orchid, Paphiopedilum armeniacum. I’d tried this species before, but always started with a rather weak plant, and looking back, they probably were all wild collected. The new plant was healthy, with very strong roots and a flower that lasted a long time – a good sign a plant is happy.

This species is known for growing long stolons between growths, unlike most other Paphiopedilums, making it difficult to keep in a traditional pot for very long. I’d seen masterfully grown plants in big flat trays and hanging baskets, and instantly wanted to try my hand at growing this species that way too. Check out this link to see the grower that inspired me to try this method: Paphiopedilum armeniacum basket culture success story.

The first season I let the plant grow in the small pot it came in, but in March of 2014, I planted it into a standard hanging basket with a coconut fiber shell (figure 1). I punctured the dense fibers of the coconut liner to allow water and the stolons of the plant to easy pass through. The growing mix was pretty standard for this species, a mix of large diameter perlite and pumice gravel, fine bark and chunks of charcoal. The plant was kept in a semi-shaded area hanging from a sasanqua bush, Camellia sasanqua, where it received plenty of summer rain and was fertilized regularly.

Paphiopedilum armeniacum 2014
Figure 1: Paphiopedilum armeniacum in March 2014.

The plant was taken in during the worst winter weather even though this species is known for enduring repeated frost. In winter watering was held to a bare minimum, but humidity levels were maintained over 50%. By the spring of 2016 the plant had grown steadily, increasing from one main growth and three smaller ones, to three adult growths and two slightly smaller ones (figure 2). Though I was encouraged that it grew fairly well, something seemed not quite right, so I decided to replant it into fresh medium.

Paphiopedilum armeniacum summer 2016
Figure 2: The same plant two years later. It looks good, but not quite thriving.

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Cycads in my home garden, July 2016

Growing cycads is a labor of love that takes a lot of patience, and failure is common. That is particularly true if try to grow species from around the world since they have a wide range of needs and tolerances. In my home garden here in southern Japan I grow species from the Americas, Africa, Australia and Asia. My success has been, not surprisingly, variable. I grow all of my collection in pots since my garden is quite small and I rent the house.

Here’s what’s going on in my cycad collection this summer, 2016.

Lepidozamia peroffskyana (right foreground), Encephalartos ferox (center), Dioon spinulosum (left back), and Zamia dressleri (pink flushed plant) – all of these plants have flushed new leaves this season except E. ferox. When growing cycads you get used to plants skipping a season for new frond growth.
Dioon spinulosum and Zamia dressleri – both plants have newly flushed growth. The Dioon has a lovely soft blue green color and the Zamia pink-bronze. Both will harden off and mature to dark green.
Zamia dressleri – his species has been really hard to keep here in southern Japan, mostly because of the colder winter conditions, even in the relative warmth of a grow room which occasionally goes down to 5 C – not to its liking. It is said this species also needs a particular mycorrhizal fungus to remain healthy long term. I can only guess this plant was inoculated with the fungus when I got it five years ago.

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The loquat tree, Eriobotrya japonica, the Japanese biwa fruit tree

The loquat tree, Eriobotrya japonica, is an evergreen broad leaf tree or shrub originally native to south-central China, being most famous for its sweet, succulent fruit. Through the years it has been established in subtropical to southern temperate regions across the world and has naturalized in many places. It’s species epithet, japonica, is in truth a misnomer since it was first encountered by a westerner, the botanist Thunberg, in that country. Regardless, the plant has gained notoriety across the globe as an ornamental tree, for its fruit products, as tea (loquat leaf tea) and to a lesser extent, as a medicinal herb.

Eriobotrya japonica is a tree or large shrub of low subtropical mountain forests, attaining a maximum height of about 10 meters. Usually single stemmed, the bark is grey-brown, with smaller branches typically covered in a rusty to grey colored “wool” (a condition known as tomentose).

Loquat Fruits
The ripe fruits of the loquat tree are produced in clusters and typically are bright orange.

The broad crown is densely branched and rounded in form. The tree’s rigid, evergreen leaves are simple, broad, serrated, and deeply veined, each growing from 10-25 centimeters long. New leaves are fully tomentose and light green. They turn dark green and shiny as they age, but remain tomentose on their undersides when mature.

The flowers are borne in loose to tight clusters from late fall into early winter, and are quite aromatic. They are small, no more than 2 centimeters across, with five white petals surrounding a yellow center. The buds as well are tomentose. The flowers are pollinated in the depths of the winter months, and by spring mature into clusters of simple, round and slightly elongated fruits, brilliant orange in color and typically no more than 5 centimeters in length. These as well are have a slight fuzz to the outer skin, but inside are fleshy, juicy and sweet. Loquat seeds, usually numbering 2-4 per fruit (though there can be up to 10), account for much of the fruit’s mass, perhaps up to one third of their total weight.

The loquat is originally native to subtropical forests of southeastern Sichuan and adjacent areas of Hubei Province in south-central China. Since ancient times it has been cultivated over much of southern China, Indochina, Taiwan, and Japan. Readily spreading from seed, it naturalized in these same areas centuries ago, effectively becoming part of the native flora. In more recent years it has been naturalized throughout the world in appropriate climates stretching from India to the Middle East, throughout the Mediterranean region, parts of eastern and southern Africa, the southern USA, throughout Central America and into South America (where it grows in the cooler highlands), Australia, New Zealand, and numerous island chains including Hawaii, Bermuda, and Réunion.

loquat tree new growth
New growth on loquat trees is light green in color and very fuzzy. This growth also contains high levels of toxins and should never be consumed.

This species is considered an invasive weed in eastern Australia (Queensland and New South Wales), throughout the southern USA, New Zealand, South Africa and on many islands throughout the world (for example, Lord Howe Island, Norfolk Island, Easter Island, The Galapagos, Hawaii, Réunion and Tonga).

E. japonica probably was first cultivated for its fruit. Like many other fruit trees, typical wild forms do not usually produce desirable fruit, so selective breeding was needed. Loquat trees are thought to have been cultivated in China for over a thousand years. This tree (known as biwa in Japanese) made its appearance as a cultivated plant during the late Edo Period in Japan (1603-1868), though wild forms with undesirable fruit likely had been brought centuries earlier. Loquats were first cultivated in Europe as early as the 1700’s. It is believed that Chinese immigrants brought the tree to the Hawaiian Islands in the late 1700’s.
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The tree dahlia, Dahlia imperialis, king of the dahlias

While many gardeners grow dahlias, few even know of the tree dahlia, Dahlia imperialis, the largest of them all. Though it can attain tree size, like other dahlias it is an herbaceous plant that dies down to the ground in cold weather. A native of Central America’s highlands, it nevertheless can be grown in fairly cold winter climates. Beyond the plant’s amazing size, the flowers are the main drawn in the garden, and they couldn’t come at a more novel time – just before the first frosts of winter hit.

Tree dahlia flowers
The flowers of the tree dahlia, D. imperialis, are borne in generous clusters just before the frosts of winter hit.

D. imperialis is a large herbaceous plant standing typically between 2-6 meters tall, with extra vigorous specimens reported to top out at 9 meters. The fleshy stems grow singly or in clumps, starting out vertical, but eventually bend in a gentle arc by flowering time. They are segmented with nodes around 30 centimeters apart, giving them a superficial bamboo-like appearance. The leaves are compound in structure and are borne in opposing pairs. They look much an elderberry leaf (Sambucus sp.), with broad leaflets that are rich green in color. Underground thickened stems form clumps of elongate tubers with relatively few wiry roots.

The flower heads form rapidly late in the season, with flowering starting in early November. Each growth can hold multiple heads of flowers, bearing 2-20 pale purple flowers 10-15 cm across. Flower color is variable, ranging from mauve (most common) to pale pink and even pure white. The flower center is orange-yellow. Double flower forms also exist, both pure white and pink.

The tree dahlia is a plant of relatively high mountains, being found above 1500 meters elevation from Mexico’s central ranges, and southward to Guatemala and Panama (some sources report them from Columbia as well). These are plants of open, sunny environments growing in well drained, yet rich moist soils. In their native range some frost can be expected, hence their adaptation of going dormant in winter.

Tree dahlia plant
By early September the rapidly growing plant slows down a bit and gets almost bushy – then in October it rockets upward again in preparation for flowering.

Growth begins relatively late, even here in southern Japan, usually not before mid May. In cooler maritime climates they may start even later. This is not a problem since they explode into growth during warm, wet weather. I’ve noticed that plants will grow up to around 2-3 meters tall by August and then they seem to slow down, becoming almost bushy at the top end. Then sometime in October they continue their rocket upward, growing another 2 or more meters higher, rapidly forming their flower heads which typically bloom around the second week of November.

One issue with this plant is its late flowering period. It seems to flower after most plants have died down and with winter just around the corner. If you live in an area where the first frosts don’t come before December, then flowering will commence normally. If however frosts hit in October or November, you’ll never see your plants flower, even if they grow normally and overwinter well. This seems to be a common complaint with plants being grown in the UK and the eastern USA in cold hardiness zones below zone 8, where early season frosts are common.
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The rain lily, genus Zephyranthes, AKA zephyr lily

The genus Zephyranthes (commonly called rain lily, zephyr lily, and fairy lily) is a group of New World bulbs more closely related to Amaryllis than the true lilies, genus Lilium. In nature these plants are native to warm temperate, subtropical, and tropical regions ranging from the southeastern USA through Central America and into South America. Due to their great beauty and vigor, several have become established throughout the warmer climates of the world including parts of Africa, Asia, Australia and even many south Pacific Islands.

In this article we’ll be looking at three commonly grown rain lilies: Zephyranthes candida, carinata, and citrina. What makes these a perfect trio is their relative cold hardiness, ease of cultivation, and variation in color – white, pink and yellow, respectively. What’s more, they are so popular that all three are easily obtained from normal garden centers, big box stores, as well as specialty nurseries.

Rain lily bulbs
Rain lilies grow from tunicate type bulbs and have grass-like leaves. These plants are Zephyranthes carinata.

Rain lily bulbs are tunicate type bulbs, similar to Narcissus, Amaryllis, and Lycoris, usually not more than 2-3 centimeters in diameter. They readily form new bulbs by offsets, which are of course genetically identical. Many also easily germinate from seed, thus they can form large, clumping colonies, sometimes carpeting the ground. Their leaves are grass-like and quite short, usually not more than 30 cm long. They are typically evergreen, but during cold snaps they can go fully dormant.

Flowers are borne singly, held in an upright position, are relatively large and showy, and have a variety of colors ranging from white to pink and yellow. Petals are uniform, broad, prominently veined, concolor, and six in number. The center of the flower is dominated by six large, elongate anthers, typically yellow to orange in color. Flowers are held just above the leaves on relatively short, fleshy scapes. Flowering ranges from spring through early autumn. Many flower most abundantly after significant rains, hence their common name, rain lily.

The following are descriptions of the three above mentioned species, focusing on their distributions (both native and naturalized ranges), habit, and specific information about each.

Z. candida – a species originally from southern South America – Argentina, Uruguay, Paraguay, and southern Brazil, having become naturalized over much of the world from the southeastern USA, the West Indies, southern Africa, southern Asia including China, Korea, Japan, as well as Australia (Queensland), and a number of south Pacific Islands. It is perhaps one of the easiest in the genus to keep happy, withstanding both fairly heavy frosts to scorching hot summers.

The flowers are pure white (sometimes blushed with pink) with a green center, bright yellow-orange stamens, and are up to 5 centimeters across. The petals are relatively narrow and pointed, giving the flower a star-like quality. The flowers commonly open en mass after heavy rains, giving quite a show. The leaves are rather thick and curled inward, giving the overall impression of a sedge or rush – another interesting feature of this species, and possibly the reason why it is relatively cold hardy.
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The windmill palm, Trachycarpus fortunei, king of the cold hardy palms

The windmill palm, Trachycarpus fortunei, is the most cold hardy of the arborescent palms found anywhere in the world – at least as far as we know. Originating from central China and adjacent parts of southeast Asia, it is grown in far flung parts of the world these days, withstanding surprising amounts of cold, wintry weather. If you’ve seen a picture of a palm tree with snow covering it, most likely it was a T. fortunei.

It has become such a common feature in “tropicalesque” temperate gardens that having one is no longer a big deal nowadays. In nature it lives in humid continental climates that range from cool to hot in summer, and quite frosty in winter. For this reason it can be grown in both hot and cool summer areas, provided winter lows don’t get too cold.

Trachycarpus fortunei pair
Trachycarpus fortunei, the windmill palm, is the most cold hardy of all arborescent palm trees.

Trachycarpus fortunei is a single stemmed, arborescent palm of relatively cool mountain forests. The trunk typically attains heights up to 10 meters (~30 feet), however vigorous ones can go 13 meters or more (a little over 40 feet). It’s trunk is quite narrow, no more than 30 centimeters in diameter, and usually covered by a thick layer of old leaf bases that look exactly like a fibrous plant husk. Some older trees have clear trunks that are grey in color.

The fronds are palmate, meaning they have a long leaf stem (petiole) that ends in a fan-like frond composed of fused leaflets. These grow up to 2 meters long, are very regular in appearance, are normally dark green, and very nearly round, hence the common name windmill palm. The petioles are nearly bare except for a two rows of small spines, and can be up to a meter long. The fan is composed of 30 to 50 leaflets, each up to 90 cm long. They can be held straight out in some trees, forming a true fan shape, or droop considerably in others (much like the leaflets of Livistona chinesis). These characteristics are consistent within a tree, and so are due to genetic rather than environmental factors.

Windmill palm trunk
The trunk of the windmill palm is literally covered by fibrous old leaf bases. These have been used in Asia as a material for fabrics.

Flowering commences in mid spring. Clusters of flowers (called spadices) emerge and elongate into downward arcing scapes up to a meter long and carry hundreds of flowers each. This palm is dioecious, meaning trees either carry female or male flowers. Flower color is creamy yellow, though the female flowers are bit more green. Male trees can also have spadices that have hermaphroditic flowers (having both female and male parts) and these can set viable seed. The kidney shaped seeds mature to a blue-black color by late fall and winter.
Continue reading “The windmill palm, Trachycarpus fortunei, king of the cold hardy palms”