I receive a lot of questions about Cypripedium seed germination, reflasking and soil media for seedlings. That which follows will provide some guidance in this area, however for the individual really serious in getting involved with the entire process, I recommend getting a copy of "North American Terrestrial Orchids Propagation and Production" if possible.
For seeding, there are a number of medias which are satisfactory for various species. Withner (1) has several. Riley (2) recommends a modified Lucke. Anderson (3) lists several. Harvais media is another one I have heard about. The one I use is proprietary, however, I don't think much different than some of the others.
Seed can be taken green pod or mature. I prefer green pod at about 60 days as it is easier to handle and it gets the seedlings off quickly (no chilling required). The parent plant likewise has more time to build its reserves and strength for next year. With mature seed, there may be dormancy factors and/or inhibitors which may interfere with germination and subsequent growth, and cold treatment is often recommended. For cold treatment, I recommend a four month chilling at near freezing to no more than 35 degrees Fahrenheit, to be on the safe side. At no time should plants or seed be placed in the freezer where the temperature gets well below freezing.
Once planted, the seed is placed in total darkness (I use boxes) to germinate. Temperature is between 65 and 70 degrees F. When the seed has formed small pin-head size protocorms, they are reflasked approximately one half inch apart in bottles. They are again placed in the dark to continue development. So far, Cypripedium irapeanum is the only one I have found that requires light at this stage for further development. Cypripedium reginae, if brought into the light at this time will form leaves and eventually a new growth, but this wastes time.
Germination may come on very heavy and development look superior, only to have the entire population die off within days. Some will germinate and produce comma-like forms which never grow any further. Germination is often sparse, even with what appears to be very good seed.
The objective of the seed germination phase and rhizome development is to produce a growth bud for the following season. Keeping them in the dark encourages this. The larger the growth bud, the stronger the seedling will be. However, they sometimes develop to a point and then die back. They must be chilled before they reach that stage. It is not a problem with most however.
Once the growth bud is about a half inch tall and as round as a toothpick, they can be chilled. For most, it takes about a year to reach this stage. Chilling can be accomplished in flask or after removing, cleaning and planting in, preferably, flats or community pots. I do not recommend planting first year out of flask seedlings in natural conditions. They are too small and fragile and often develop rot and are lost. Chilling is explained above.
For most species and hybrids, I have found that coarse vermiculite one half with coarse perlite is a superb media for seedlings just out of flask, even growing them to maturity. This media is proving to be very satisfactory for even some of the more acid types as Cyp. guttatum and Cyp. acaule hybrids. [One exception to this is that Cyp. kentuckiense can be grown is sandblasting sand (silica sand primarily) immediately. Mature plants of this species are grown in it as well.] Cypripedium acaule has not been tried in vermiculite/perlite mix, and I question whether it would work for it or not.
The seedings are grown in 75 percent shade or about 20 inches below florescent tubes. They are kept fairly wet in the early spring, tapering off later to keeping them damp. When watering, water thoroughly and wash any accumulated salts or phenols out of the media. Replace the vermiculite/perlite mix annually. Fertilize in the spring and early summer with one-quarter strength fertilizer - Peters, etc., or half strength Dyna-Gro.
The plants will often go dormant on their own. Outside, they can get frosted off. Or they can be put in the refirgerator after about six months of growth. Check the size of the new growth. It should be nice size by then. My seedlings are grown in plastic boxes with holes drilled for drainage. I put the top on them, put them in a plastic bag, then into the refrigerator. This keeps them from drying out - the media should be just damp, not wet. Chill as above.
It is interesting that some of the initial seed germination work was done with Cyp. acaule, with 100% mortality when removed from flask. This species is by far the most difficult to grow, so it is no wonder there was such a failure rate for seedling. I find that germinating Cyp. pubescens is extremely difficult. I believe that some of the species are more selective regarding the media on which they will grow, and this can explain some of the germination problems.
Note that in this and other writings I refer to Cyp. pubescens, Cyp. parviflorum and Cyp. calceolus as different species. This is in the horticultural sense only. I will not get into the taxonomic argument about it. They are distinct in their culture and several genetic aspects. When someone says they are growing Cyp. calceolus, the first thing I have to ask is which one. Using these as species names, recognizing that we are speaking horticulturally, will save a lot of confusion and lost time. It is important to note that they are recognized as separate species in the hybrid registrations.
(1) Withner, C.L. (ed) 1959 The Orchids: A Scientific Survey. New York: Ronald Press.
(2) Riley, C.T. 1983 In: Plaxton E.H. (ed), North American Terrestrial Orchids, Symposium II, Proceedings and Lectures. Southfield, MI: Michigan Orchid Society.
(3) Anderson, A.B. 1990 In: North American Native Terrestrial Orchid Propagation and Production, Conference Proceedings March 1989. Chadds Ford, PA: Brandywine Conservancy.
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