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, wintery 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 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.
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.
The exact native range of T. fortunei is not well known since it has been cultivated for centuries in China and Japan. Most sources list it as being native to elevations of no more than 2400 meters anywhere south of the Qin Mountains of Shanxii Province in north-central China, and westward through Sichuan and up to the edge of the Tibetan Plateau, with the apparent main distribution having been in the Yangtze River Valley. The species is also reported from Myanmar, Vietnam, India, Nepal, and Bhutan, where it is most likely naturally occurring. It is found in Taiwan and southern Japan, but its occurrence here is most likely a product of cultivation.
Nowadays this palm is found usually near human habitation, so the exact habitat type it originated in is unknown. It is found near cultivated fields, as yard trees, in plantations and occasionally in forests. It is most commonly seen in warm temperate to subtropical mountains or hills throughout its range.
In cultivation this palm has been grown even in areas with distinctly cool temperate climates including much of Europe (as least as far north as the UK, Ireland, Belgium, Holland, France, Germany, Denmark, southern Scandinavia, and westward to Bulgaria and Crimea), North America (north to coastal British Columbia, Canada and coastal areas of Washington State and southward, and in the eastern USA as far north as coastal Virginia and the deep south states), as well as Tasmania and New Zealand (where it is considered an invasive species). Here in Japan it is naturalized to low mountain forests, and though volunteer seedlings even show up occasionally in my small garden, I wouldn’t call it a pest species.
Much has been written about and asserted concerning the limits of this plant’s ability to endure cold. It is not uncommon to hear of people growing it in truly cold winter climate areas such as southern New England, the southern midwest states, and the southern plain states in the USA. Mind you these areas rate as cold as USDA zone 5 many winters.
Despite these reports, without some fairly serious winter protection, this palm isn’t likely to endure anything lower than -12 C (10 F) and remain a viable plant in the longterm. Still, that is very impressive for a tall trunked palm. Can a mature, well sited specimen endure colder temperatures and live? Sure, perhaps. Severe cold snaps, if fairly short in duration, most likely will be endured, but there is a limit to this as well.
Of course, if you wish to go the extra mile and protect your trees, you can extend its growing range remarkably farther north provided the soil only superficially freezes. With that in mind, this palm is fully cold hardy up to USDA hardiness zone 8 (even in cool summer climates), and with good winter protection can certainly endure zone 7, and possibly even zone 6 (there are plenty of folks who said they’ve succeeded). Anything colder than that and you’ll need a greenhouse or equivalent winter protection.
Folks cook up all kinds of novel ways of keep their palms alive in winter including completely wrapping them with fleece or cloth, making miniature greenhouses around the whole tree (sometimes just the crown), protecting the crowns with straw or similar materials, knocking snow off the fronds, mulching the ground around their bases, and even wrapping their trunks with Christmas lights! These methods can work wonders, but as you can imagine, as trees grow it becomes increasingly more difficult to protect them. There is a whole wonderful world of “zone deniers” out there that will go to almost any length to keep their prize plants alive in less than perfect conditions.
With cold hardiness out of the way, let’s consider other needs of this palm in the garden. It grows very well in full sun if the roots are well watered, but the fronds will tend to grow more compact. In a more sheltered spot the fronds will be longer and the tree will have an overall cleaner look on average. This tree also does fairly well in moderate shade, though in truly deep shade it will be spindly and unhealthy. Some growers report that the foliage will shred fairly easily in windy climates, making them unsightly (you really can’t please some people!).
In nature it most commonly grows on well developed loam soils, though this does not seem to be a requirement as trees do quite well in the sandy soils of north Florida. Likewise, clay soils do not seem to be much of a problem since this tree is commonly grown in the southern states of the USA, famous for their red clay. The Royal Horticultural Society’s website even lists chalk base soils as adequate. Soil reaction is optimal from medium acid to around neutral (~pH 5-7), though this tough palm can handle more acidic or alkaline conditions as well. It certainly thrives in Japan’s acidic, volcanic loam soils. Fertilizer can be applied (especially in potted specimens), but most soils have enough natural nutrition to keep this tree happy. Propagation is from seed, which is said to be rather straightforward.
Diseases are thankfully not that bad for this palm. Occasionally scale and aphids can cause infestations. Root rot is a problem and can cause the tree to die suddenly and completely, but this condition is rare (I do see this fairly often in wild trees in the forests of Japan though). Leaf spot can also be a problem, but mostly is unsightly. Harrison and Elliott list T. fortunei as moderately susceptible to lethal yellowing (a systemic bacterial disease). Though incurable, the disease has been successfully controlled with oxytetracycline HCL (OTC). Trees have to be treated repeatedly, and even if the bacteria are suppressed enough to allow normal growth, reinfection may occur.
A few interesting details about this palm. It was first introduced to Europe by the famous German physician/botanist Philipp Franz von Siebold in 1830, presumably the first westerner to see this species. Oddly enough, it wasn’t described until 1850 under an illegitimate name, and later in 1861 by its present name. Though Siebold was the first to discover this palm, it was the Scottish plant collector Robert Fortune working for the Royal Horticultural Society who brought the palm into England in quantity starting in 1849, and hence it was named after him. Interestingly, Kew had received a seedling from Siebold’s original collection as early as 1836. It is odd how some things work out.
T. fortunei has been cultivated for centuries in China and Japan mostly for the fibers derived from the old petiole bases. Especially in times past these were used to create fabrics, brooms, brushes, and doormats. The fruits are also a source of wax and a hemostatic drug (eFloras.org).
Until recently, a dwarf growing compact form, ‘Wagerianus’, was considered a separate species. Currently most botanists do not consider it distinct from T. fortunei, probably in part due to the fact that no known wild populations exist (and therefore no type material for botanical analysis). It was found in cultivation in Japan a couple centuries ago, and little is known about its true origins. Regardless, it is very distinctive in appearance, and is true from seed, so for growers it is definitely a different palm. It is much more compact in all respects and coveted as a garden plant, being called “much prettier than fortunei” by most growers. Luckily, it seems no more difficult to grow than the typical type, and is just as cold hardy. Truly, this palm deserves a separate article.
Here’s the perfect cold hardy palm if you just can’t live without that tropical look. Moderately fast growing, with few requirements other than a relatively mild climate, this palm’s a winning candidate for tropicalesque gardens everywhere.