Introduction to Lady Slipper Orchids
Cypripedium (aka Ladyslipper Orchids) are by far, the showiest and most popular of the hardy terrestrial orchids. There are 48 species total in northern temperate land masses around the world...the majority in East Asia. There are 11 species of Cypripedium native to the United States, found in every state except for Florida, Hawaii, and Nevada....sorry, folks. One species, Cypripedium reginae (showy lady slipper), is the state flower of Minnesota.
The name Cypripedium comes from a mix of Latin and Greek. It alludes to Cyprus, the island that was the mythical birthplace of Aphrodite (Venus) and "pedilum", a shoe or slipper (or feet), and so literally means Aphrodite's Slipper. The genus Cypripedium contains only the cold hardy slipper orchids. Tropical slipper orchids are placed in the genera paphiopedilum, mexipedium, phragmipedium and selenipedilum.
Cypripedium are composed of either a basal set of leaves, or a leafy stalk to 2' tall. The Cypripedium flower, which tops the stalk or rosette, is an enlarged pouch called a "lip" or a "slipper", backed by three long, dark-colored, twisted petals. The slipper can be as large as a chicken egg or quite small depending on the species. The North American Cypripedium species are clump-formers while some of the Asian species spread around the garden via rhizomes.
Unfortunately, the majority of Cypripedium sold in the US are still dug from the wild. Fortunately, the trade in nursery propagated plants is growing larger every year, although the price will never be able to compete with wild collected plants. Cypripedium grown from seed usually take from 6-8 years to reach flowering size, so when you see flowering size plants sold for less than $35, you can be pretty sure that they have been wild collected. Some specialty nurseries are selling young Cypripedium seedlings for less money, but since it is extremely difficult to have good survivability with young seedlings, be sure you're able to properly care for young plants.
How to Grow Lady Slipper Orchids
Cypripedium are generally considered to be difficult plants to grow, but within the genus, some of the North American species such as Cypripedium kentuckiense and Cypripedium parviflorum var. pubescens are among the easiest. Not only should growers in the warmer climates focus on these species, but also the hybrids using these species should be good choices in warmer regions. The most common reasons for Cypripedium failure are poor soil preparation and incorrect planting techniques. Some Cypripedium prefer dry, sandy, acidic soils, while others prefer moist, neutral or alkaline soils. If there is a question about what conditions a Cypripedium needs, the default is a moist, well-drained, organically rich soil with a slightly acidic pH. Unlike other garden plants, Cypripedium roots don't actually grow into the ground. In the wild, their roots lay flat on top of the ground and are then covered with natural compost. If Cypripedium are planted like other plants, especially in unprepared soils, they will die. When we plant Cypripedium in the garden, we prepare the soil, bare root the plants, and then stretch the roots out horizontally on the soil. The roots are then covered with compost and followed by mulch. Since the roots are shallow, be sure they don't dry out until the plants are well established.
There has been a bit of talk about the role of mycorrhizal fungi in the survivability of cypripediums. The research now appears to show that mycorrhizal fungi are essential in the seed germination of species such as Cypripedium acaule, but does not appear to be required for their growth. Stay tuned, as research into their role continues.
Some Cypripedium have an unwelcome trait in skipping growth some years. For reasons still not fully understood, a Cypripedium may simply decide not to grow one season, but will return just fine in subsequent seasons. Other than finding a good plant therapist, there isn't much that can be done to solve this, so don't give up on your lady slipper just because it remains underground.
List of Cypripedium species
Cypripedium acaule (Pink Lady Slipper Orchid)
Although many folks think ladyslipper orchids are rare, Cypripedium acaule is anything but. This Eastern USnative hails from almost every state east of the Mississippi including Canada. In the wild, it is typically found in acidic well-drained pine or hardwood forests. Cypripedium acaule consists of a basal set of two leaves, topped in mid-spring with a 1' tall spike, ending in a pink pouch. Cypripedium acaule is one of the most difficult species to transplant and cultivate in the garden, but this should be made easier as this species is finally being grown from seed in nurseries. (Hardiness Zone 2-8)
Cypripedium cordigerum (Heart Lip Lady Slipper Orchid)
This Himalayan ladyslipper (China, Nepal, Bhutan, and Pakistan) is found from 6500 - 12,000' elevation in forests where it grows in moist, slightly acidic to nearly neutral soils. The 2' tall leafy stalks are topped with large white pockets backed with yellow-green sepals. (Hardiness unknown)
Cypripedium fasciolatum (Striped Lady Slipper Orchid)
This Chinese species hails from the Sichuan, Hubei, and Guizhou provinces of China, where it grows at elevations between 6000 and 7500'. The large white flowers with chartreuse sepals are nearly as large as the American Cypripedium kentuckiense. (Hardiness unknown)
Cypripedium flavum (Chinese Yellow Lady Slipper Orchid)
Cypripedium flavum is a Chinese species, native to moist alkaline soils along forest edges and open grasslands at 5600-11,000' elevation in Yunnan, Sichuan, Xizang, Gansu, and Hubei provinces. The 15" tall stalks are adorned with 6-10 leaves and topped with yellow pocketbook-like flowers, each backed with purple-stained yellow sepals. (Hardiness unknown)
Cypripedium formosanum (Formosa Lady Slipper Orchid)
This is a very rare high mountain Taiwanese ladyslipper orchid similar to Cypripedium japonicum. The spectacular, heavily pleated green leaves resemble a Japanese hand fan opened horizontally atop 6" tall stems. Held just above the foliage is a scrumptious dark pink lady slipper-like flower. When happy, Cypripedium formosanum forms a nice clump, spreading by underground rhizomes. Cypripedium formosanum is the more heat tolerant equivalent of the cold loving Cypripedium japonicum. Cypripedium formosanum prefers moist, well-drained slightly acidic to slightly neutral pH soils. Light shade with a couple of hours of early morning sun is best. (Hardiness Zone 6b-9)
Cypripedium henryi (Henry's Lady Slipper Orchid)
This small growing species is native to forest margins in the Chinese provinces Gansu, Guizhou, Hubei, Shaanxi, Sichuan, and Yunnan at 2500-7000' elevation, and prefers moist, organic, alkaline soils. Each 18" tall stalk is topped with 2-3 small chartreuse-green flowers. This is relatively easy to grow compared to many of the other Chinese species. (Hardiness Unknown)
Cypripedium japonicum (Japanese Lady Slipper Orchid)
The spectacular, heavily-pleated green leaves resemble a Japanese hand fan opened horizontally atop a 6" tall stem. Held just above the foliage is a scrumptious pink lady slipper-like flower. These are not easy to grow and should only be tried by very serious gardeners and plant collectors.
One of the best examples that I've seen in the eastern US is a wonderful clump at the US National Arboretum in Washington DC. Light shade and slightly acidic soil are best. (Hardiness Zone 4-7a at least)
Cypripedium kentuckiense (Kentucky Lady Slipper Orchid)
Native from Virginia west to Texas, the southeastern native Cypripedium kentuckiense has performed wonderfully for us, making large 18" + tall clumps, topped in early to mid-May with large, creamy, pocketbook-shaped flowers, highlighted by dark purple twisted sepals, and adorned with yellow flecking. These have been very easy for us to grow in light shade in a slightly acidic to slightly alkaline pH. (Hardiness Zone 3-8)
Cypripedium macranthos (Macranthos Lady Slipper Orchid)
This species has a wide distribution from eastern Russia to China, Korea, Japan, and even Taiwan, where it can be found in grassy slopes and at forest edges. The 20" tall stalks are topped in late spring with large pockets of violet. Rich, organic soils around a neutral pH are best. (Hardiness Zone 4-7a)
Cypripedium montanum (Northwest Mountain Lady Slipper Orchid)
This northwest US native is often found growing in open coniferous forests from 1500-6500' elevation. The vigorous growing clumps are composed of 2' upright stalks, each topped with 2-3 white pocketbook flowers and highlighted by reddish-brown sepals. (Hardiness Zone 5-7a, at least)
Cypripedium parviflorum var. parviflorum (Small Yellow Lady Slipper Orchid)
(aka: Cypripedium calceolus var. parviflorum)
This is a Midwest/east coast woodland native that can be found in wet boggy soils to dry hemlock forests. Some taxonomists segregate the far northern form as Cypripedium parviflorum var. makasin. In very late spring, the 1' tall upright stems emerge clothed with large fuzzy leaves. As they finish unfurling, you will find them topped with an exquisite, bright yellow, small pouch-like flower, backed with long mahogany sepals. Once established, the clumps will develop into multiple stemmed prizes worthy of including in your will. Cypripedium parviflorum is quite easy to transplant. (Hardiness Zone 4-7)
Cypripedium parviflorum var. pubescens (Large Yellow Lady Slipper Orchid)
(syn: Cypripedium calceolus var. pubescens) The giant yellow lady slipper orchid is an easy-to-grow native that ranges from the northern Midwest south to North Carolina. Cypripedium parviflorum var. pubescens makes a large clump (with age) of 20" tall stalks, clothed with hairy green leaves. In May the clumps are topped with amazing bright yellow "ladyslipper" flowers...several times larger than Cypripedium parviflorum var. parviflorum. Where I grew up in Raleigh, this was prevalent on dry slopes in deciduous forests, although it can be also found in wet open meadows in the northern part of its range. Like regular Cypripedium parviflorum, this subspecies is also easy to transplant and grow in the garden. (Hardiness Zone 3-8a)
Cypripedium reginae (Showy Lady Slipper Orchid)
The showy lady slipper is one of the most abundant northeast US species. In June, the plants emerge with 18'' tall stalks, each clothed in oblong velvety leaves. From mid-June to July, the stems are topped with small, but exquisite slipper flowers...white sepals at the top with a pink slipper attached below. In time, Cypripedium reginae will develop into quite a large clump. Cypripedium reginae prefers a partially open site with a moist, neutral, or slightly acidic soil. (Hardiness Zone 2-7a)
Cypripedium reginae 'Alba' (White Showy Lady Slipper Orchid)
This gem is a very rare white flowered form of the treasured US native, Cypripedium reginae. Cypripedium reginae is one of the latest species to emerge in spring, but when it does, the 18" tall stems are topped with white pocketbook-like flowers in late June or early July depending on your climate. (Hardiness Zone 2-7a)
List of Cypripedium Hybrids
Great strides have been made in the last 25 years in Cypripedium breeding. The first Cypripedium hybrid was registered in 1987 by Carson Whitlow of Cyp Haven in Adel, Iowa. Today, there are over 130 registered cultivars. Other important breeders include Paul Keisling of Massachusetts, Owen Robinson of Raising Rarities in Jacksonville, Vermont, Peter Corkhill of the UK, Werner Frosch of Germany, Heinz Pinkepank of Germany, and Svante Malmgren of Lidafors Garden Orchids in Sweden. Collectively, their goals are to improve hardiness, improve ease of culture, increase flower size and discover new color combinations.
Cypripedium cultivars are almost all exclusively seed grown, with the cultivar names representing all plants from a particular cross. While the plants are similar, each clone will be slightly different with regard to the intensity of the coloring, the floriferousness, the growth rate, and number of flowers per clump.
Cypripedium 'Aki' (Aki Lady Slipper Orchid)
This strain of hybrid lady slipper orchids was developed in 1996 by Germany's Werner Frosch by crossing the Chinese Cypripedium macranthos with the American Cypripedium parviflorum var. pubescens. The heat tolerance of the Cypripedium parviflorum var. pubescens allows gardeners in warmer climates to have success.
The hybrids, which display amazing vigor, emerge in late spring forming 18" tall stalks topped with large plum to pink striped flowers, each highlighted by three twisted pinkish sepals. (Hardiness Zone 4-7, probably colder)
Cypripedium 'Aki Pastel' (Aki Pastel Lady Slipper Orchid)
This new and highly sought after hybrid ladyslipper orchid is a cross of the Chinese Cypripedium macranthos with the American Cypripedium parviflorum var. pubescens. The 18" tall stalks are
topped in late spring with large flowers which consist of a "slipper" of white, backed by three twisted yellow sepals, each highlighted by small cinnamon specks. (Hardiness Zone 4-7, probably colder)
Cypripedium 'Emil' (Emil Lady Slipper Orchid)
This 1993 Werner Frosch hybrid of the European Cypripedium calceolus x the American Cypripedium parviflorum var. parviflorum is a vigorous grower, topped in late May with 18" stalks of stunning flowers, each composed of a bright yellow pouch complimented by dark burgundy, twisted sepals. A well-grown clump of Cypripedium 'Emil' can produce up to 24 flowers in only 3 years...fastest in cool summer climates. Cypripedium 'Emil' is named after Emil Lueckel, former president of the German Orchid Society. (Hardiness Zone 4-7, at least)
Cypripedium 'Gisela' (Gisela Lady Slipper Orchid)
This 1992 Werner Frosch hybrid is a cross of the Chinese Cypripedium macranthos x the American Cypripedium parviflorum var. parviflorum. This robust grower makes a patch of 15" tall stems, each topped in mid-May with a creamy yellow pouch with burgundy streaks, backed by three large sepals of dark burgundy with a flush of yellow. (Hardiness Zone 4-7, probably colder)
Cypripedium 'Gisela Pastel' (Gisela Pastel Lady Slipper Orchid)
This is a selection from the same cross that gave rise to Cypripedium 'Gisela' (Cypripedium macranthos x Cypripedium parviflorum var. parviflorum). This plant was selected for its creamy yellow pouch, backed by three large yellow sepals with streaks of dark burgundy. In May (NC) they are topped with 15" stalks of flowers. (Hardiness Zone 4-7, probably colder)
Cypripedium 'Hank Small' (Hank Small Lady Slipper Orchid)
This 1991 Carson Whitlow hybrid is the result of a pre-arranged rendezvous between the US native Cypripedium parviflorum var. parviflorum and the Chinese Cypripedium henryi. This easy-to-grow selection produces 18" tall stalks topped in mid-spring with a rich, deep yellow pouch, backed by long, twisted cinnamon sepals for a stunning contrast. The hybrid is named for its parents. Hank is a common name for one parent Cypripedium henryi, and Cypripedium parviflorum means "small". (Hardiness Zone 4-7)
Cypripedium 'Inge' (Inge Lady Slipper Orchid)
This 2003 Werner Frosch hybrid combines the vigorous genes of Cypripedium parviflorum var. parviflorum with the large flower size of Cypripedium fasciolatum. Atop the 16" stalk of this mid-season bloomer, enjoy a long-lasting creamy pouch about the size of a small egg, highlighted by amber-purple handlebar moustache-like sepals. Cypripedium 'Inge' is fast to form a nice clump. (Hardiness Zone 4-7)
Cypripedium 'Ingrid' (Ingrid Lady Slipper Orchid)
This 1990 Werner Frosch hybrid strain is a cross of the Chinese Cypripedium cordigerum and the American Cypripedium parviflorum var. parviflorum. The 18" tall stalk is topped with a creamy white pouch, backed by three twisted cinnamon/maroon sepals often suffused with gold. Cypripedium 'Ingrid' is named after German orchid grower Ingrid von Ramin, who in the 1970s was one of the pioneers in the cultivation of native European cypripedium. (Hardiness Zone 4-7, at least)
Cypripedium 'Kristi Lyn' (Kristi Lyn Lady Slipper Orchid)
This 2003 Paul Keisling hybrid of Cypripedium pubescens x Cypripedium henryi boasts large pure yellow pouches with striking brown striped sepals and tepals. (Hardiness Zone 4-7a)
Cypripedium 'Maria' (Maria Lady Slipper Orchid)
This 1991 Werner Frosch hybrid is a cross between Cypripedium parviflorum var. parviflorum and Cypripedium macranthos var. speciosum. The result is a vigorous hybrid which, in mid-spring, produces 14" tall stalks of flowers with white pockets, occasionally stained with burgundy near the top, then complimented by twisted sepals of dark burgundy. (Hardiness Zone 5-7, at least)
Cypripedium 'Michael' (Michael Lady Slipper Orchid)
This 1998 Werner Frosch hybrid, named for cypripedium grower Michael Weinert, is a small-growing hybrid created from a cross of two Chinese species, Cypripedium henryi and Cypripedium macranthos. The 10-12" tall stalks, adorned with pleated green leaves, are topped in late spring with a stunning purple and white pouch, backed by three dramatically striped purple and white sepals. Slightly alkaline soils work the best. (Hardiness Zone 5-7a)
Cypripedium 'Paul' (Paul Lady Slipper Orchid)
This 2009 Werner Frosch hybrid of Cypripedium parviflorum var. parviflorum and Cypripedium franchetii makes a nice clump, topped in mid-spring with 13" tall stalks of creamy-white pockets surrounded by twisted burgundy-cinnamon sepals. (Hardiness Zone 5-7, at least)
Cypripedium 'Philipp' (Philipp Lady Slipper Orchid)
This 1996 Werner Frosch introduction is a hybrid of the Chinese Cypripedium macranthos and the large-growing American Cypripedium kentuckiense. Cypripedium 'Philipp' makes a robust hybrid to nearly 2' tall, topped in late spring with large slippers of white with maroon spots near the top, backed by stunning large deep purple sepals often streaked white. (Hardiness Zone 4-7, at least)
Cypripedium 'Rascal' (Rascal Lady Slipper Orchid)
This 1990 Carson Whitlow introduction is a hybrid of Cypripedium parviflorum var. parviflorum x Cypripedium kentuckiense. The blooms are mid-sized, yellow with twisting brown sepals. (Hardiness Zone 4-7, at least)
Cypripedium 'Sabine' (Sabine Lady Slipper Orchid)
This 2002 hybrid from Germany's Werner Frosch combines the Chinese Cypripedium fasciolatum together with the Chinese Cypripedium macranthos. Atop the 18" stalk sits an obscenely large, Grade A egg-sized flower, composed of a light pink pouch, backed with purple and white striped sepals. (Hardiness Zone 5-6)
Cypripedium 'Sebastian' (Sebastian Lady Slipper Orchid)
This 1998 Werner Frosch hybrid, named for cypripedium grower Sebastian Urban, combines the genes of the east coast Cypripedium parviflorum var. parviflorum with the northwest US native Cypripedium montanum. This long distance romance resulted in vigorous 23" tall plants that produce narrow flowering stems topped with white pocketbook-shaped flowers, backed by prominent twisted red-burgundy sepals. The Cypripedium montanum parent passed along both a slight fragrance and the multiple flowers per stalk trait. (Hardiness Zone 4-7a, at least)
Cypripedium 'Tower Hill' (Tower Hill Lady Slipper Orchid)
This 2003 Paul Keisling hybrid (Cypripedium parviflorum var. pubescens x Cypripedium macranthos var. speciosum) is a similar cross to Cypripedium 'Aki'. The clump forms 18" tall, erect flower stalks, topped in mid-spring with large pocketbook-like flowers of creamy white flushed with burgundy. The pocketbook is backed by three slightly twisted cinnamon and gold sepals. (Hardiness Zone 4-7)
Cypripedium 'Ulla Silkens' (Ulla Silkens Lady Slipper Orchid)
This vigorous, stunning 1996 hybrid from Svante Malmgren is a cross of the American Cypripedium reginae x the rare Chinese Cypripedium flavum. Cypripedium 'Ulla Silkens' is much easier to grow than its parents and will take a good bit of sun in cooler climates, but still prefers moist alkaline soils. The 2' tall flowering stalks that appear in mid-to late-June are topped with huge slippers of burgundy and white, backed by three large pure white sepals. The clumps will become quite large with nearly 100 flowers per clump. (Hardiness Zone 3-7)
Cypripedium 'Victoria' (Victoria Lady Slipper Orchid)
This 2005 Peter Corkhill hybrid combines the US native Cypripedium parviflorum var. pubescens with the Asian Cypripedium fasciolatum. The resulting vigorous hybrid produces stalks topped with a creamy white pouch backed by light brown sepals. This is a similar cross to Cypripedium 'Inge' except for using the larger flowered form of Cypripedium parviflorum. (Hardiness Zone 4-7)
Cypripedium x ventricosum (Siberian Hybrid Ladyslipper Orchid)
This rare orchid hails from Siberia, Cypripedium x ventricosum was long thought to be a new species, until research showed it to be a natural hybrid of Cypripedium calceolus and Cypripedium macranthos. The slippers range from lavender to brown, depending on which parent contributed the most genes, and the same goes for the 3 sepals...purple to brown striped. (Hardiness Zone 4-7a at least)
I hope this article has taken some of the mystery out of the genus Cypripedium and hope you now feel inspired to try some of these magical garden plants. Please keep in mind that these are best tried by gardeners who take their gardening seriously. They are not plants which can be crammed into a hole dug in unprepared garden soil...save your money for impatiens if this is your level of gardening. If, on the other hand, you like a real challenge, Cypripedium orchids are for you. Good luck and enjoy!
Berliocchi, L., et. al., (2004), The Orchid in Legend and Lore, Timber Press, Portland Oregon, Pg. 56
Case, M.A., et. al., (1998), Conservation Genetics and Taxonomic Status of the Rare Kentucky Lady's Slipper: Cypripedium kentuckiense (Orchidaceae), American Journal of Botany, 85(12): pp.1789-1786
Cribb, P. (1997), The Genus Cypripedium, A Botanical Magazine Monograph, Royal Botanic Gardens, Kew and Timber Press, Portland Oregon
Doherty, J.W., (1997), The Genus Cypripedium, North American Ntive Orchid Journal, 3(1), pp. 5-120.
Mathis, W., (2005), The Gardener's Guide to Growing Hardy Perennial Orchids, The Wild Orchid Company, Doylestown, Pennsylvania
Native Orchids of the United States, online at http://www.orchids.org/ooc/na_orchids/us_orchids_java.shtml
Romero-Gonzalez, G., et. al., Orchidaceae, in Flora of North America, Vol 26, pp. 15, 16, 17, 26, 490, 491, 616, http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=10638
Setton, S.H., Tao of Orchid, http://www.sungsooksetton.com/page15/files/tao-of-orchid.pdf
Tullock, J., (2005), Growing Hardy Orchids, Timber Press, Portland, Oregon
Wilson, M., Medicinal Plant Fact Sheet: Cypriedium: Lady's slipper orchids, The North American Pollinator Protection Campaign and The Pollinator Partnership, http://www.pollinator.org/Resources