The following is a list of all known generally accepted naturally occurring lady slipper orchids, genus Cypripedium, and their cultivation status. No doubt in the coming years more hybrids will come to light, especially from China’s vast western mountains. Each year new plants are being found there that suggest hybrid origin, but as yet remain undescribed by science. There indeed is even a chance that a few unknown species yet reside there, tucked away in some inaccessible niche. The focus here is on Cypripedium availability on the world market, how challenging their cultivation has proved, what their specific needs are, and where plants have been sourced to date.
Since information is constantly changing and many growers are tight lipped about their doings, the following cannot be inclusive of all plants in cultivation. What is offered is a product of my own discussions with growers, scientists, “stuff off the grape vine”, and my own personal experience. I have avoided addressing the legality of any particular species, but suffice it to say that many plants have made it into the trade via illegal smuggling. This leaves a big question mark on the status of plants in countries that are signees of CITES since all are covered under this treaty.
The USDA zone recommendations given are not to be taken as a strict guideline. In cooler summer climates such as the Pacific Northwest of the USA or most of the British Isles, many species can be grown even in what qualifies as zone 9. Like other temperate terrestrial orchids, Cypripediums as a rule do not like hot roots, so areas with hot summer nights are unlikely to be good places to grow any of them, but a few might persist if grown optimally.
So, without further adieu, here is the first half of the list. The names highlighted in blue are clickable links to more comprehensive pages about that plant.
acaule – this species is widely cultivated from both wild and artificially produced plants. This plant cannot grow in typical garden soil, requiring very high acidity (pH <4.5). Sandy, open, pine humus rich composts have been effective, but still have to be watched very carefully for increases in pH. The best method devised so far is watering regularly with a solution of acidified rainwater (household vinegar is fine – 1 or 2 teaspoons per gallon). Use only clean rainwater, RO water, or distilled water since the plants cannot endure salt build-up in the growing medium. Avoid planting in the ground in regions with sweet soils since keeping pH down is nearly impossible. If fertilizer is used, use a very dilute solution or add nutrients via natural matter such as composed pine needles. A very difficult plant to maintain in the long term even within its native range, but possible. USDA zones 2-7.
x alaskanum – the natural hybrid of C. guttatum and C. yatabeanum from the Aleutian Islands of Alaska. Grow as per C. guttatum. Occasionally offered. USDA zones 2-5.
x andrewsii – the natural hybrid between C. candidum and C. parviflorum v. parviflorum. Seems to enjoy quite a bit of sun, at least in the morning, and any near neutral soil will do nicely. Widely cultivated from lab propagated plants. Easy. USDA zones 3-7.
arietinum – widely cultivated, but difficult and rare. Sandy compost with conifer humus will do provided it remains open and free draining. Acidity should be between pH 5 to 7. It is susceptible to rots, so avoid saturated conditions. While it is very cold tolerant, it is also incapable of enduring long periods of summer heat. Plants tend to reach flowering age much quicker than most species or hybrids. USDA zones 2-5.
bardolphianum – a few in cultivation virtually all from wild collected material. Nobody’s saying very much about them. Probably an open compost that favors inorganic components is best with a pH near neutral. Protect from winter rains, but water generously in spring and early summer. Word is they are much easier than members of section Trigonopedia, a group it is closely allied. USDA zones 4-6.
calceolus – widely cultivated especially in Europe. Mostly nursery propagated in origin, but some still coming out of eastern Siberia. European plants seem to prefer alkaline conditions, but those of Siberia grow in more acidic soils. Compost should be free draining. Touchy in cultivation, but doable in a cool climate. USDA zones 4-6.
calcicola – a few in cultivation with virtually all sourced out of the wild. Inorganic based compost is preferred. Protect from winter rains. In high latitude cool climates this plant enjoys sunshine, but grow more shady further south or where summers get hot. Not as easy as C. macranthos, but can be grown in a cool climates. A synonym is C. smithii. USDA zones 3-5.
californicum – widely cultivated from lab propagated plants. Due to very narrow habitat preferences, this species remains difficult to grow and flower. The plant itself can endure very hot conditions, but the substrate must remain cool, not higher than 18 C (65 F), and cooler is better. A well draining, organic based compost is fine, but watch for possible rots. Some growers have found it to be better growing in purely inorganic substrates, such as pumice, provided it gets fertilized well. It is reported to take a long time to grow into blooming sized plants. It is not likely to be very frost tolerant, especially in high latitudes. All in all, touchy in cultivation taking a long time to establish. USDA zones 6-7, possibly colder with thick winter mulch.
candidum – widely cultivated and fairly easy once established. Recently transplanted specimens often wilt in sunny conditions, but established ones won’t provided the substrate is moist. This is a plant of alkaline, moist prairies, so use a well draining, good loamy soil that is always basic in reaction (pH 7.5~8). In most cases lime should be added yearly to ensure a high pH. Sunshine is needed for good growth and flowering, but watch overhead midday sun. In the wild it is often found growing embedded in grasses and weeds, providing it both support and at least some shade. Seedlings are very tiny and need close attention early in development. Lab propagated material is fairly common with many turning out to be mixed blood with C. parviflorum. USDA zones 4-6.
x columbianum – the natural hybrid of C. montanum and C. parviflorum v. pubescens. Probably prefers cooler conditions and a well draining compost nearly neutral in reaction. Not widely grown, but reported to be much easier than C. montanum. USDA zones 4-6.
cordigerum – untold thousands of wild plants were exported to Europe, America, and Japan in the 60s, 70s, and 80s. Most died, but a few persisted and today a few lab propagated plants are available. Another plant that favors a nearly neutral, mostly inorganic compost. Avoid winter rains. Culture is difficult with this one with most growers saying that plants often die even after being well established. USDA zones 5-6.
debile – widely grown from both wild collected and lab produced stock. It seems to grow and even flourish for periods only to go into decline. In nature the roots grow between layers of slowly decomposing leaves and conifer needles, so an acidic compost rich in light, free draining humus should work. The pH can vary a bit between acid to neutral conditions. Since the plants are so small they cannot endure drying at all. Humidity also must be maintained at all times. It is fussy, delicate, and hard to keep alive long term. Pots only for this one unless you have perfect woodland conditions and can protect them from predators. USDA zones 6-7.
dickinsonianum – as with other members of section Irapeana, this one is essentially impossible even in their native lands. Perhaps a few smuggled specimens are available from time to time in the states and Europe. USDA zone 10 or higher.
elegans – unavailable and untried as far as I know. Nobody is talking about them in cultivation.
fargesii – lab propagated plants are becoming available in Europe and even the USA. This plant seems to be the easiest of the large leafed species in the section Trigonopedia. In the wild it grows near streams and soils can be even soggy at times (very different from other members of this section). I would avoid wet conditions in culture, keeping them evenly moist instead. An inorganic based substrate is called for and protection from winter rains is warranted as well. Still rare in cultivation, but it should become more common in time. Having said that, it remains difficult to grow. USDA zones 6-7.
farreri – a number of plants have been exported out of China since the mid ’90s, mostly to Europe and Japan. The vast bulk of these have turned out to be C. fasciolatum. It is being grown in Europe and more recently America, but is not generally available. Holger Perner is growing this species for export out of China recently (2013). They seem much more touchy in cultivation compared to the near relative C. fasciolatum. Inorganic based, circum-neutral compost with winter rain protection are probably good suggestions for cultivation. USDA zones 5-6.
fasciolatum – widely cultivated from both wild collected, and more recently, artificially propagated plants. Cultivation seems straightforward: free draining compost favoring inorganic materials, winter rain protection, and perhaps preferring a longer, warmer growing season than most western Chinese species. Still difficult to get in the states, but available in Europe and Japan. USDA zones 5-8.
fasciculatum – few have tried to grow this one and fewer still have succeeded. Sand/conifer humus compost that is perfectly draining and mildly acidic seems to be a good choice. Allow little or no summer rain on this one and dry conditions (without drying the roots) or plants tend to rot. Climates with humid conditions and warm summer nights are antithetical to this species. Very difficult to grow and maintain. A few seedlings are offered each year here and there. USDA zones 5-6.
x favillianum – the natural hybrid between C. parviflorum v. pubescens and C. candidum. This hybrid is becoming more available in the trade, but remains expensive. Grow as you would its counterpart hybrid, C. x andrewsii. Easily grown lab propagated plants are available in North America and Europe. USDA zones 5-7.
flavum – widely cultivated from both wild and artificially propagated plants. Culture is more difficult than its near relative C. reginae, but possible. It requires cool summer temperatures not exceeding 26 C (80 F) on average or the plants will go into decline. Inorganic based compost that is free draining and nearly neutral can be used. Recent information suggests that adding dolomite or oyster shell to the compost may increase vigor since wild plants seem most numerous and healthy in areas where limestone is near the surface of the ground. Not easy to get in the states, but fairly common on the European market. Seedlings have proved to be slow in growing to flowering size. Lovely, but a bit tough to keep on average. USDA zones 5-6.
formosanum – widely cultivated from mostly nursery propagated divisions and lab produced seedlings. Very easy to grow in just about any free draining, acidic to neutral compost. After a couple years stabilizing, plants will double in the number of growths yearly forming lovely colonies in time. The biggest problem is early growth especially in climates that get frequent spring frosts. This species starts growth before most other Cyps, usually around late March, with flowering occurring sometime in mid April. Therefore plants in growth must be protected from frost events or the flower buds will be lost and the plants set back a bit. It seems equally happy in the ground or in pots. Another bonus is heat tolerance. It can withstand very hot conditions in summer and requires only a cool down in winter, with 4-10 C (~40-50 F) for two or three months being adequate for dormancy. These are heavier feeders than most species Cyps – a weekly regimen with dilute fertilizer should be fine as long as the substrate is frequently flushed. What is remarkable is that this plant remains a little difficult to obtain, especially in the states. Very easy in milder climates, but cannot take very cold winters. USDA zones 6-8.
forrestii – a few wild collected plants are being grown in Europe and possibly North America. This plant is very closely allied to both C. bardolphianum and C. micranthum, so cultivation seems possible by diligent growers. Grow as per C. bardolphianum. Generally still unavailable in the trade except as wild collected plants. USDA zones 4-6.
franchetii – widely cultivated, but remains quite rare in collections. Both wild collected and lab produced plants are available today. Similar requirements to C. tibeticum and C. calcicola and probably about as easy to grow, that is, a bit tricky. USDA zones 4-6.
froschii – not widely available, but a few wild collected and cultivated divisions offered each year. It can be found in both European and North American collections very infrequently. It needs conditions like its cousin, C. tibeticum. In nature this plant is found in forest settings while C. tibeticum is often seen in very open areas, such as grasslands. Recent information points to the possibility that this species is in fact an ecotype of the highly variable C. tibeticum. Not easy and not hard to grow. USDA zones 5-7.
guttatum – widely grown and moderately available. Two groups of plants are currently being cultivated: high mountain forms from SE China and Alaskan plants. Some Alaskan plants are potentially of mixed blood, that is, hybrids or back crosses with C. yatabeanum. It is easy to grow in cold winter/cool summer climates, but otherwise is nearly impossible to grow in hotter areas. Forms large colonies in time from underground stolons. USDA zones 2-4.
henryi – widely grown and becoming more available in the US market. Many are wild collected, but many have been lab propagated too. Reported to be very easy, but given to going into decline for no known reason. Plants have been reported from subtropical mountains and also central China, so it is possible the different ecotypes exist. Having said that, USDA zones 5-7, possibly 8 for the warmer growing forms.
x herae – unusual natural hybrid between C. reginae and C. parviflorum v. pubescens. Very rare in the wild (found only in Canada so far) and very rare in the trade. Probably fairly easy to cultivate. USDA zones 3-6.
himalaicum – along with C. cordigerum, many thousands have been taken from the wilds of Himalayan countries over the last 40 or more years, and few if any, have survived to this day. This plant may be in cultivation somewhere, but again, no one is saying much about it. It seems to need something folks just can’t provide. A few plants are offered in Europe from time to time, and without a doubt, are wild sourced. Some of these have turned out in fact to be forms of C. tibeticum, so buyer beware. USDA zones 4-6.
irapeanum – along with C. dickinsonianum and C. molle, this species defies any attempt at being cultivated long term. Nobody seems to understand why exactly. Seedlings have been artificially produced, but none having been deflasked, have been grown on compost successfully. Reports out of Germany suggest someone there has been successful and even flowered some seedlings, but no photos have been made public and this remains doubtful, at least for now. At best it is a very, very difficult species that remains unavailable. Plants have been wild collected and exported from Mexico since the late 1800s even unto this day, but no reliable reports of surviving specimens exist. USDA zones 10 and higher.
Here’s the link for Part II