Growing Cypripedium Seedlings
By Peter Corkhill
In 1993, when first considering Cypripedium seedling cultivation, I was told by a Swedish friend, Svante Malmgren, that to succeed flowering terrestrial orchids from seeds you needed a lot of patience, a lot of luck and a very long life! This is good advice and I could have added, you also need to be an eternal optimist and have quite a deep pocket but in the last few years more and more people have succeeded in flowering Cyps bought as seedlings and as these have become more readily available so the price has dropped to a more realistic level. Although there is much still to learn about growing these plants, the basic information is now available to enable most of us to have a fair chance of success and, if it was too easy, we would have to look elsewhere for life's little challenges!
There are a number of advantages in buying Cypripedium seedlings as opposed to mature plants. The first is that you can be very sure that newly deflasked seedlings with nice white roots and fragments of agar still clinging to them, have not been collected from the wild to further deplete threatened populations. If we want to continue to grow this genus into the future then artificial propagation from legitimate seed sources is the only answer and the expertise gained may well fuel future attempts to restock wild areas where species have become extinct from habit destruction and over collection.
Treating deflasked seedlings
Seedling quality is the first factor to consider when buying. Depending on the species a good newly deflasked seedling should have a number of roots up to several inches long and at least one well formed bud. Generally bud size is a good indicator of vigour but a few species and hybrids have quite small buds which never the less have potential to produce good leafy shoots under the right conditions. If there are traces of agar, wash the seedlings to remove this but never scrub the roots or try to wash off the staining that sometimes accompanies the use of certain flasking media.
Ideally, buy your newly deflasked seedlings in the Autumn so you can supervise their winter quarters yourself and then you can be sure they are properly vernalised. These seedlings, with the possible exception of C. formosanum, all require a cold period of at least four months before they will reliably produce leaves in the Spring. However, research with C. reginae has shown this species will respond to shorter vernalisation periods but it is still better to give a normal winter. There are a number of ways of doing this and I can only recommend the methods that have worked for me. Seedlings can be sealed into polythene bags (freezer quality) with a drop or two of clean water and placed in the salad compartment of a normal household fridge, preferably the right way up and making sure it is the roots and not the buds that are in contact with any free moisture. Alternately, the seedlings can stand in sealed rigid food containers again with a few drops of water or rest on top of a damp layer of Perlite. Inspect the plants every few weeks for signs of mould growth. If this occurs you can treat with a suitable fungicide such as Physan to prevent further spread and isolate infected individual seedlings. Normally, mould does not grow on healthy undamaged tissue but occasionally sections of root start to die off in flask and this is susceptible. Don't use too much water inside the container, just enough to provide a constantly humid atmosphere, not wet conditions. Never allow the seedlings to freeze, a temperature between 2 and 4C is ideal.
It is also possible to pot up seedlings when they arrive in Autumn and winter them naturally in a frost free greenhouse or cold frame. I prefer not to do this because everything is out of sight and I like to know what is going on with the plants. Also, newly deflasked seedlings are susceptible to invasion by fungi and/or bacteria and some of these are pathogenic. The longer a seedling has to fight off this invasion before bursting (no, sneaking!) into growth, the more chance there is of failure. Some growers recommend placing potted seedlings in bags in the fridge for vernalisation but when I tried this they all failed, no doubt the compost was too wet and rot set in. Also the space requirements in the fridge are much greater.
All this may seem a bit fussy but it is only necessary during the first winter. After that winter the seedlings in their pots and follow the instructions given under caring for adult potted plants.
Potting
Pot up the seedlings during late February or March, water them in and place in their growing quarters keep frost free but do not apply any extra heat. If you feel tempted to plant out your new seedlings in the open gardenright away, don't! Save your money and buy some hardy annuals instead. I prefer plastic pots but have used clay with success too but the latter have to be plunged into soil, peat or damp sand to prevent drying out too quickly, at least where I live. Conditions inside the pot have to remain as steady as possible so larger pots are preferred to small ones and don't stand them where the sun will warm the growing medium. Personally, I never use a pot smaller than 4 inches even to pot a single seedling and conditions are more even in an 8 inch pot planted with 4 or 5 seedlings where the survivors can remain until flowering size without disturbance. Plastic plant troughs, cat litter trays or even polystyrene fish/vegetable boxes are also used with success with the right drainage holes but this is more in the realm of large scale production. Whatever container is chosen, ensure there are plenty of drainage holes and with the deeper containers (more than 2 or 3 inches deep) place a layer of course drainage material at the bottom of the pot. A piece of shade cloth at the bottom can help stop compost/drainage material running out and also helps stop unwanted guests getting into the pot from below.
Composts
When I first started growing Cyp. seedlings I had the idea that success depended on finding the "correct" compost formula but with more experience I now know success can be achieved on some very different mixtures and really depends on finding the mixture that suits your particular growing conditions and watering habits. Conditions can even vary from one side of the greenhouse to the other so to make recommendations about compost mixtures for other people is not realistic. It is best if I indicate what are the characteristics of a successful compost and what materials can be used to provide these but the individual must experiment and find by trial and error, what works for them.
A seedling compost must above all be free draining, that is free draining enough so that when water is pored into the top of the pot it runs right out of the bottom. At the same time, it must remain evenly moist and not dry out so the use of water retentive materials is indicated. In nature, orchids mainly grow on low fertility sites so the mixture must not provide high levels of initial fertility or components which break down rapidly releasing nutrients. Also it should not contain a high concentration of organisms which have the potential to promote disease such as actively decaying organic matter.
Mixtures containing ingredients such as Seramis, pumice, coarse Perlite, coarse vermiculite, horticultural grit and coarse silica sand (Cornish grit) can all provide the correct physical conditions within the mixture and the proportions and choice of these will depend on local availability, cost and individual preference as well as the local conditions to be catered for. German growers have had good success using mixtures based on Seramis which provides good water retention in areas with higher summer temperatures and lower atmospheric humidity but I find in the damp and cloudy north-west of England that this mixture is too wet and in fact does not dry fast enough to allow enough liquid fertiliser to be given over the course of the summer to promote growth. Under these conditions Seramis must be diluted by at least 50% with less water retentive materials like pumice (2 3mm) or Perlite (super-coarse grade). In our damp climatic area, I have had good results using Perlite alone as the inorganic fraction of the compost, and also succeeded with a mixture of 50:50 Perlite: Cornish Grit. Some other growers prefer mixes containing some vermiculite to prevent surface drying which can be a problem when Perlite is used. Topping the composts with a layer of alpine grit or a material such as Hydroleca (burnt clay granules) gives more even surface conditions and helps suppress growth of algae which is sometimes a problem but this makes it harder to know when to water.
When seedlings do die it is usually the crown area at the base of the shoot where problems start and roots continue to look healthy, after the top of the plant has died. So environmental conditions in the top 2 cms of the compost are critical, too wet and rot will be encouraged, too dry or intermittently drying out, will lead to desiccation. Hence, where you house your seedlings will also have a dramatic effect on whether they live or die as well as the compost mixture and your watering habits.
Good seedling compost should, in my experience have a ratio of 4 or 5 parts by volume of inorganic components to one part of organic matter and the seedlings given occasional extra nutrition in the form of dilute liquid fertiliser. The choice of organic matter is again up to the individual but beech humus, leaf mould, composted chipped wood, composted bark have all been used successfully. Beech humus is my current favourite but is not available everywhere. This is the layer that occurs under the most recent layer of fallen undecayed leaves and contains decayed and partly decayed leaves, fragments of tree roots and the native soil. If the trees grow in a limestone or chalk area ,so much the better, as this will ensure the compost that results is slightly alkaline and all that remains is to sieve the material to remove large roots, stones and unwanted guests.
Pine duff is a similarly excellent material and comprises the layer of pine needles in various stages of decay under the most recent layer. However, it seems the pine trees must be growing on a sandy or dryish soil for this process to occur and so far I have failed to find suitable material in the north of England where most pine trees grow on wet peaty soils. Pine duff is acidic so mixtures containing this should also contain lime in some form to bring the compost pH up to neutral or slightly alkaline. The exception is for mixtures to grow C. acaule which should contain some peat to acidify the compost, otherwise peat should be avoided.
Other leaf mould should only be used with caution as it can be rather soggy, retaining too much moisture and decaying quickly releasing nutrients too fast which blacken delicate root tips. Composted bark which is available at most garden centre outlets can be used with excellent results but it is a very variable product and if the composting process has not been carried out correctly then it continues to decay and contains many fungal hyphae, some of which could well be harmful.
I have never tried sterilising seedling composts believing that it wasn't necessary and that sooner or later the seedlings would have to encounter life in the big wide world. However, I do wonder if inoculation with a symbiotic fungus, isolated from Cypripediums somewhere, would confer a degree of protection against harmful organisms at weaning if introduced to the seedlings just before deflasking. To date I haven't had access to such a fungal culture or come across anyone who has.
Housing
If you have grown tropical orchids in the past you may be at a disadvantage when learning how to manage Cypripedium seedlings but growers with a background experience of alpines may fair better. Best results have been achieved in cool greenhouses, shade-houses or coldframes placed in a shaded or semi-shaded positions or by growing in cool cellar-like conditions under artificial lights.
Protection from rain is an advantage as it enables you to know how much water and nutrients the seedlings are receiving but the first delicate leaves are also prone to scorching by sun and drying winds. Good ventilation is required to keep pathogens such as botrytis at bay but high even humidity (not less that 60% is ideal) can be difficult to maintain if the ventilation is too efficient and will lead to composts drying out when your back it turned.
Good housing will also make it much easier to protect your developing plants from the many predators that will seek them out in the open garden such as molluscs, mice, voles as well as larger animals like blackbirds, moles, rabbits, squirrels and cats that invariably find terrestrial orchid beds fascinating.
Management
To water or not to water? That is the question! I generally water seedlings into the compost after planting and then store them until growth starts by placing in a frost free, cool, moist environment like a cellar or under greenhouse staging. Under these conditions it is not normally necessary to water again for a couple of months or so. When growth starts water with extreme care and never saturate the compost. Later in the season when leaves are full sized and tougher, you can water and fertilise more freely but reduce again in Autumn and keep just barely moist over the winter months (see advice on managing adult plants). It is a good plan not to allow pots to freeze solid in the winter months and minimum temperatures of 2C are adequate in providing conditions for proper vernalisation.
Dilute fertilizer (about one quarter normal strength) needs to be applied regularly when the plants are in growth and occasional flushing through the compost with clean water will wash out accumulating salt deposits. Bear in mind that your water will already contain some fertilizer depending on its source and this will affect the amount you have to add. Buying a salts meter which measures the total dissolved solids, is to be recommended and a fertilizer strength of 300 micro-siemens regarded as the maximum safe dose for young seedlings. Choose a balanced fertilizer that has the major ingredients in roughly equal proportions and contains trace elements. I have been told that fish emulsion is very good but have not tried it yet myself.
Keep the growing area free of pests such as slugs, aphids, sciarid flies etc and as clean as possible removing all decaying plant material which would encourage fungal infections.
If after three or four years your seedlings have made good growth then is the time to try experimenting with growing in the open garden. However, remember when trying anything new it takes at least a year before you can evaluate the effects, so proceed with caution, it is a slow learning curve!
Waiting
In any batch of 20 seedlings there are always one or two that seem to grow at twice the speed of the rest and these precocious seedlings may exceptionally produce flowers in 3 or 4 years. However, in general one should expect to wait 5 or 6 years for the majority and perhaps up to 10 years for temperamental individuals. Some hybrids seem to be more vigorous than the species they derive from but if you are wanting to grow species then you must be prepared to wait and have failures. The answer is to buy a batch of seedlings each year so you always have young plants in various growth stages.
Sources of Plants
There are now quite a number of specialist nurseries offering Cypripedium seedlings within Europe and North America and these may be found on the Internet or advertising in the pages of Alpine Plant Society magazines. Each year the range of hybrids and species offered increases but to avoid difficult importation regulations it is easiest to buy locally. Within Britain there is an actively growing Hardy Orchid Society and members usually have the chance to buy plants at meetings and shows.
Check out their website at http://www.hardyorchidsociety.org.uk