Notes on the Artificial Cultivation of Cypripedium formosanum
By Carson E. Whitlow*
Of the hardy terrestrial lady-slippers, Cypripedium formosanum is one of the easiest to cultivate. It is adaptable to pot culture and its dormancy does not appear to be totally dependent on near freezing temperatures. It is also on of the nicest appearing in both flower and plant.
The two leaves of Cyp. formosanum arise very early in the spring. They are round and fan shaped, nearly opposite each other. The upper one is usually a little smaller than the other. They are atop a stem six to ten inches tall. From between the leaves a four- to eight-inch stem carries the single flower.
The lip of the flower is large and inflated, similar to Cyp. acaule. The entrance to the pouch, which for the Cypripedium species is usually through or around the staminode area, is closed in this species. A circular opening on the forepart of the lip is provided instead. The sepals and petals are similar, being oblong-lanceolate, although the sepals are slightly broader. The diameter of the flower reaches three and a half inches or so. All segments are white. An overlay of purple pin dots radiates from the center of the flower, and is generally focused on the central part of the flower. The interior of the lip and around the opening into the pouch are striped with the same coloration.
The rhizome is one of the longest of the Cypripedium species, often six inches between growths. Thus, the container in which they are grown must be fairly large. Eight-inch azalea pots have been recommended1 and plastic dishpans are known to have been used. Mine are grown in cut down rose cones or other large diameter styrofoam containers, ten to twelve inches tall. Roots form beneath the forming new bud only, not all along the rhizome. Two new growth buds a year is common. The rhizomes are planted about three inches deep. When dividing, the entire bud and rhizome portion is kept together.
Various media are used for growing this species. Most are mixes used for Paphiopediums or similar species. Hach(1) suggests a mixture of medium fir bark, peat moss and styrofoam chips with two inches of osmunda fiber on top, in seven-inch pots. Mine are potted in rotted pine needles with some sand added. In nature, Fowlie(2) noted they grow under and through rotting leaves, well drained. The medium is kept constantly moist. In spring, during growth, it is kept wetter, while in the fall and winter it is kept a little drier; it is never allowed to dry out. Fertilizing is with quarter strength general purpose fertilizer every couple of weeks. For light, full shade or under the benches in a greenhouse is appropriate. Outside, they should be protected from wind.
Cypripedium formosanum is quite hardy, tolerating Iowa's hard winter. Unfortunately, it wants to begin growth in February and March, often during our mid-winter thaw, only to be destroyed by the return of freezing weather a few weeks later. When the thaw was very early or failed to penetrate the mulch, or when we failed to have one, the plants literally were the first up and blooming. This habit of breaking dormancy so early limits its distribution in outdoor gardens to those areas not having below freezing weather after that time, or where there is no mid-winter thaw. Protection from frost in early spring also needs to be considered.
Under greenhouse conditions, in pots, the plants begin growth in February-March to bloom in April. On the other hand, if kept in a cool area, the growths will come up a half inch or so and sit there until warmer conditions are given. They must be kept from freezing once they have begun to grow.
In the fall, the plants will go dormant normally in October-November in the greenhouse. Outside, the frost will do the job. Then, they are placed in a cool, frost-free area to over-winter. However, this cold treatment does not seem necessary. Brubaker(3) indicates that all that is needed is a rest, and a 50 F. minimum temperature seems sufficient.
Riley(4) indicates that the seed can readily be germinated in quantity. Hybrids have shown fair germination. In hybridizing with this species, two distinct lines may well develop. One line will require little dormancy and adapt readily to pot culture, while the other will be more suitable for outdoor culture.
1. Hach, Dieter. Growing "Lady's Slippers" in the garden. Orchid Review, Vol. 85, No. 1009, November 1977, pp. 340-343.
2. Fowlie, J. A. The Quest for Cypripedium formosanum Hay. In Formosa (Taiwan). Orchid Digest, Vol. 48, No. 1, January-February 1984, pp. 4-9.
3. Brubaker, M. M. Cypripedium formosanum. Orchidata, Vol. 13, No. 2, 1974, p. 31.
4. Riley, Clark T. Hardy Orchids - Horticultural Seed Germination and Commercial Potential. Proceeding from Symposium II & Lectures, Michigan Orchid Society, 1981.
* as it appears in the ORCHID DIGEST, Vol. 51, No. 4, Oct.-Nov.-Dec. 1987, Page 180.
Since this article appeared, I have found that a commercial product, "Ball Growing Mix 2," is a very good potting media for this species. C.E.W.
Fine Fir Bark 4 Gal.
Sphagnum (teased apart but not cut up) 1 1/2 Gal. packed
Fiberized Redwood 1/2 Gal.
Agway Shell Firmer 1/2 Gal.
Haydite, 1/4" 1 Gal.
Gypsum 1/4 Cup
"Bovung" 1/2 Cup
Bone Meal 1/4 Cup
Dolomite Limestone 1/4 Cup
(After 1 1/4 years use with my acid water, the mix had a pH of 6.4).
Carson E. Whitlow
2291 - 280th Street
Adel, IA 50003