The following is taken from a very reputable commercial nursery Vermont LadySlipper Company http://www.vtladyslipper.com/vtlscwebpg11.html that raises and sells Lady Slippers
Q.I've heard that you need a special mycorrhyzae fungus in your soil to grow these . Is this true?
Cypripediums, like all orchids, begin their life cycle when their seed (pro-embryo) is invaded by a microscopic fungus (endophyte). Since orchid seed has no endosperm (stored starch reserves that kick start most other plant species), the fungus in essence forms a surrogate root system for the seed.
If the soil nutrient levels and pH are correct, the fungus becomes a symbiont and provides small amounts of carbohydrates to the growing seed(protocorm). This is a very delicate process whereby the fungus infiltrates the growing orchid seed to a certain stage and then the orchid seed defensively responds by producing a group of chemicals that actually dissolves the fungal filaments back.
After having its filaments dissolved, the fungus will then reattempt to invade the protocorm and supply more carbohydrates and the protocorm will grow again ever so slightly. This process is repeated until the protocorm has grown large enough to produce a small dormant eye bud and root system (seedling). Once this occurs, the following spring the cypripedium will produce it's first green leaf and begin to use photosynthesis as its primary energy source. Once the seedling relies on photosynthesis, the cypripedium will reject the micro-fungus almost completely. This heterotrophic phase can take anywhere from 3 to 7 years to occur in nature. It can take an additional 5 to 10 years to reach flowering size which means the Cypripedium can take anywhere between 10 to 17 years to bloom, in the wild, from initial seed dispersion!
This above heterotrophic growth sequence only occurs when all the habitat and soil conditions are right. This is the primary reason for the natural rarity of cypripediums and not that the fungal symbiont they use is rare. Indeed, under many soil conditions, the fungus that the orchid requires can become a pathogen and destroy the orchid seed. There are several micro-fungi that have been isolated in cypripedium roots and the truth is that there are probably many more that could perform the symbiotic function given the right soil conditions.
Adult cypripediums do not require this fungus. We know this as a fact because we have grown 10's of thousands at Vermont Ladyslipper Company without it. We germinate the seed and grow the seedling in sterile agar cultures with plant nutrients and sugars to completely bypass the fungus requirement in infancy. These are the same techniques that are presently being used to produce large commercial quantities of tropical orchids.
Therefore, if you have a healthy adult cypripedium (Many for sale at Vermont Ladyslipper Company of Course!) and know the soil and pH requirements for the species in question, you can grow any cypripedium successfully in a garden without it's corresponding micro-fungus.
All this being said though, it is still of the utmost importance for all gardeners to do what they can to save what remains of natural cypripedium habitat so the genus can survive into the future. At this point the world needs to save and actually repair what has been lost of our natural environments. Orchids are wonderful indicator species to show us how much still needs to be done. Therefore,we are actively encouraging people to attempt to start new colonies in promising habitats with our plants that may reproduce naturally and actually BOOST the number of Cypripediums. We believe that we can actually stop and reverse the decline of this genus by applying our knowledge base and production techniques.