Svante Malmgren Henric Nyström
|Cypripedium species and hybrids|
propagation and growing
The genus Cypripedium really does deserve a chapter of its own in any narrative about terrestrial orchids. The plants have an exotic appearance and of the approximately 45 species in the world some can be grown with success in gardens in regions with cold winter climates. With a little special care to site specimens in well-drained soil and semi-shade, several species and many modern hybrids can live for very many years just like other garden perennials growing into bigger and bigger plants every year.
Unfortunately, the beauty and the rarity of cypripediums have ignited a profitable illegal trade in plants of wild origin. Most countries nowadays try to regulate this trade with more or less success. It is regrettable that many horticultural enthusiasts have contributed to this illegal trade either knowingly or in ignorance.
For these reasons there is a strong incentive to propagate Cypripedium plants artificially, not only not only to grow larger numbers of specimens at more reasonable prices, but also to produce modern amazing Cypripedium hybrids, which make the wild plants less commercially attractive.
The enhanced supply of Cypripedium plants will also increase knowledge regarding the best ways of cultivating them. Some of the wild species are easy to grow, but others seem almost impossible to keep alive even in the hands of expert growers. An increase in the supply of easy-to-grow hybrids will in time make cypripediums much more common garden plants.
We shall here describe how to grow cypripediums in the garden, but in order that the reader may understand the possibilities and difficulties it is also necessary to describe how propagation is done. Of course, this includes growing from seed on sterile media, but also how to care for small seedlings during their first few years in soil. This knowledge makes it easier to understand the demands of adult plants. A description of the propagation procedure also explains why some species and hybrids are available on the market in quite large numbers and some not at all. It will also tell you why you should not select a plant solely on the basis of a flashy picture on the Internet ...you also need to find out if the cypripedium in question is hardy, if it grows well in cultivation and if it is legal.
Propagation from seed
Propagation from seed is done principally in the same way as with other orchid species described on the website. In the genus Cypripedium, however, both in the case of species and hybrids, there is a very wide range between those that are “easily propagated” and those that are “almost impossible”. Unfortunately, the ease of propagation does not correlate with the beauty or rarity of a particular plant.
Several factors may determine whether or not a particular plant may be “easily propagated”. Is there an adequate supply of the seed? Can the seed be sown mature or does it have to be half-mature? Does the seed respond well to your growth medium? Is the seed from a self-pollinated plant viable? Is one species genetically compatible with another so that fertile hybrid seed may be produced? Do the plants grow well in your climate and on the soil that you provide? The Cypripedium propagator must be prepared to answer all these questions, have great patience and a long life expectancy.
In a single seed capsule of Cypripedium guttatum there are 500-1,000 seeds, Cypripedium calceolus produces 1,000-1,500 seeds per capsule and Cypripedium flavum about 4,000. Hybrids can produce anything from zero to thousands of viable seeds.
Some Cypripedium seed germinates easily when mature, for example the seed of Cypripedium guttatum, parviflorum, flavum, reginae, acaule, passerinum, californicum and hybrid seed where one of the cited species is the mother plant. A proportion of these species germinate within a few weeks but others will only germinate following a three month chilling period post-sowing.
Other Cypripedium species will only germinate at all on sterile media if the seed is sown half-mature. Some may to an extent appear to germinate normally from mature seed, but subsequent growth is often poor and it is obvious that inhibitory factors are present that affect more than just germination. When sowing of half-mature seed is successful 75-100% germination may occur within weeks and later growth may be strong ...if the medium is appropriate. It can be difficult to assess exactly when the seed embryos in the green capsule are indeed “half-mature”. The rate of maturation of the seed is dependent on variable factors such as summer temperature and presence or lack of rain. Furthermore, the interval between immaturity and over-maturity can be as short as 5-7 days. In Sweden where we live, most cypripediums have half-mature seed embryos about 8 weeks post-pollination.
Poor seed availability and a less than ready supply of fully grown seed-producing plants might also be restricting factors. If you want to sow half-mature seed successfully, the mother plants cannot be growing any great distance from your laboratory or home. Certain individuals, moreover, have defective pollen and seed production might be disappointingly low as a consequence. Inbreeding as a result of self-pollination rarely causes problems with the other orchids described on this website, but we have strong suspicions that some of the problems encountered in Cypripedium propagation are a result of this. In many cases, a cross between different clones or subspecies produces much more viable seedlings than does selfing. This appears to be especially true in the Cypripedium macranthos group and possibly also with Cypripedium tibeticum.
Many species germinate and grow very satisfactorily on the medium we described earlier, especially with the addition of a small piece of potato and 1-5% pineapple juice. Some species and hybrids germinate and grow very well on this medium until they are de-flasked, but others need minor changes to the fresh medium when they are moved from the sowing vessel. We continue to encounter a few species that germinate excellently, but then 95% of the protocorms die when they reach 2mm in size ...the survivors, however, grow on perfectly normally. The proportions of organic and inorganic nitrogen in the medium, together with the amount of plant hormone and organic complex can affect the result substantially. If you read scientific reports about Cypripedium propagation from seed, study carefully how the nitrogen source, plant hormone(s) and organic complexes are combined. Different species might well prefer different combinations and these preferences probably also vary according to the age of the protocorms.
Thus, if the intention is to propagate all the cypripediums, obvious deficiencies remain in the media we are using. Our results, however, may be interpreted as highlighting the fact that different cypripediums have variable propagation requirements. The field is still wide open for an ongoing trial and error process. A few decades ago nobody had propagated Cypripedium. Werner Frosch was first with Cypripedium reginae and Svante Malmgren was probably the first to propagate Cypripedium calceolus on a large scale.
There are not many people in the world with much experience over a long period ...and if we try to use each others’ methods, results often continue to be poorly reproducible.
When hybridising, it is extremely important not only to select two good species, but also to choose the right individual parent plants within the species – something that can only be done, of course, retrospectively. The actual choice of parent specimens from each species greatly affects the results obtained. This phenomenon, well known in the micropropagation of other plant species, can be frustrating for the small scale Cypripedium propagator.
Is the hybrid going to be a good one? It will take 3 to 4 years after sowing before you will know if the plants grow strongly on soil as well as in vitro and 5 years before you will know if you have produced a beautiful flower. Very many Cypripedium hybrids are poorly viable and we have created several hybrids that never reached flowering size and finally died. Many of the registered Cypripedium hybrids have been raised only in very small numbers. On the other hand, it is amongst the successful crosses that you will find the most easily grown cypripediums, the plants whose shoot number increases most year by year and those with flowers of the most spectacular size and colours.
Growth on media
If the seed germinates according to plan and the plants grow on normally, they will need to be transferred to fresh medium once in their in vitro life ...just like the other orchids described on the website. 3 to 5 plants may be grown per 20-25ml of medium in order that optimal size and number may be obtained. The total time for growth on medium is 7-(10)-15 months, depending on which species or hybrid you grow. Some hybrids and a few species develop very quickly on medium whereas others need a long time to develop long roots and a shoot for the subsequent growing season.
When they reach this point they must be given a resting period of at least 3 months, close to zero degrees C; if the temperature is significantly higher, then even longer is needed. If you are unlucky, inadequate vernalisation can mean that the plants will never start to grow in soil. In spring 2008, approximately 400 plants of tibeticum and macranthos types, potted in soil, died for us, due to poor vernalization during the extremely mild winter in Sweden that year…
Potting up in soil can be done at any time during the cool resting period but the easiest way is to keep the young plants on medium during the winter ...that way they will take up less space and need less care. We usually pot them in soil very early in the spring whilst the temperature remains fairly low. They prefer to keep cool, but frost-free, for a few weeks more.
You can place them directly outside in soil, but there is always the risk that bad weather may harm them while they are still small and sensitive. It is preferable to start them into growth in a cool, shaded greenhouse or under artificial lighting in a chilly room. Good ventilation is most important, as is keeping the temperature low, especially at night. Cypripediums dislike high temperatures, especially when they are little with small shoots and short roots!
Soil for seedlings?
As described elsewhere on the website, we always use “natural” soil. For Cypripedium seedlings we use the top 10cm layer of a soil derived from mixed coniferous and deciduous woodland. The soil is naturally well draining and we always use clay pots. This combination provides good drainage and good close contact between the roots and the soil. The clay pots are plunged in damp peat which maintains suitable moisture conditions in the soil.
It is only possible to learn how to look after small cypripediums during their first year on soil by making mistakes. Once experience has been gained, though, 90-100% of the plants should survive. In most cases they either nearly all survive or they all die ...if you have made a significant mistake.
In the late summer, the clay pots containing the plants can be placed in a shady part of the garden (beware birds and snails, though!) and you can start thinking about where to keep them over the colder months. We keep our potted plants on benches over the winter. See later for photographs.
Soil for fully grown cypripediums?
Cypripediums can be grown in many different kinds of soil in your garden. As experience is limited and not very widespread, many mysterious compositions and myths regarding them can be found in the literature. Whether your soil is slightly acidic, slightly basic or neutral, whether it is of a largely mineral or a mainly organic composition, the most important factor is that it be well drained! Soil that is too wet or too compact in combination with heavy autumn and winter rain is probably the commonest cause of death in the garden. Sometimes it might be necessary to change the soil locally in the garden or, even better, place the cypripediums in an elevated flower bed or on a slope. Cypripedium calceolus is not that uncommon in the wild where we live, but in all its sites it always grows on very compact, clayish limestone soil that is as hard as concrete when dry and like mud when wet. But it always grows on slopes so that excess water runs away. We have never seen any Cypripedium growing on perlite in the wild, so seek your own successful method in your own garden using a suitable soil.
Moreover, of greater importance is how to place the plants in soil. Cypripedium plants, small as well as fully-grown, always produce next year’s bud in late summer and autumn at the soil surface or even above it. Thou shalt not cover this bud with wet, compact soil. It must be protected in some way, though, against birds, heavy winter frosts and strong, spring sunshine. In nature this function is performed by dry leaves and conifer needles and in the garden we must use a substitute of some kind.
One easy method is to cover the buds with a little sand or fine gravel. In areas with heavy autumn and winter rain, covering the buds with a roofing tile or similar is probably necessary for young plants and beneficial for adults.
In the spring the new shoots quickly burst into life and the gravel can be removed or left to improve drainage.
Where in the garden?
All cypripediums have large but thin leaves, indicating a preference for a position in weak light or semi-shade, or at the very least not in direct hot sun. Small plants are particularly sensitive and even those adult plants that can tolerate more sun grow best in half-shade. Some species and hybrids, especially Cypripedium flavum and Cypripedium reginae have hairy leaves and tolerate more sun, but the flowers can burn and become damaged by strong sunlight. A growing position under a small, coppiced tree is usually good, but do remember that deciduous trees produce leaves rather late in the spring and the sun can be very strong in April. Cypripediums much prefer to grow in a cool spot to a warm one!!
Adult plants or young ones?
Nowadays, it is possible to purchase several different Cypripedium species and hybrids via the Internet and via a number of specialised nurseries in many countries. The propagators, however, are very few in number and most salesmen are just salesmen and increase the price by 100-200%. Fully grown flowering sized plants, 5 years of age, might then cost from 35-70 euros each.
Our recommendation is that growers should buy and try 3 year old plants. These have been grown on soil for 2 years and must have spent one winter outside, proving their vitality, and they should grow on well. They can be purchased at a proportionately lower price. Just remember that small plants have shorter roots than adults and are therefore more susceptible to damage from drought and strong sun during their first year on soil.
Also remember that from the propagator’s point of view, certain species and hybrids are easy to raise in large numbers but other species and hybrids will only be produced in 5-25% of the quantity for the same amount of effort put in. Therefore, there is a pretty good availability of some sorts and a very limited supply of others.
Do all you can to avoid buying illegally imported plants. Do not support the eradication of wild cypripediums!!!
Can mature plants be divided?
In most cases the straight answer is “no”. Large plants can be split but do not be too greedy and avoid making too many divisions. It is easy to damage the rhizome and to break many roots and shoots.
Planting with companion plants in the garden
This is mainly a question of personal taste and aesthetics. Some cypripediums bloom for no more than 7-8 days whereas others bear flowers that last for more than 3 weeks. After flowering there are just a lot of big leaves ...you may find these beautiful or you may not. Avoid planting cypripediums very close to trees and bushes as their roots might compete with those of your orchids. On the other hand, shade or semi-shade is undoubtedly beneficial.
From seedlings to flowering plant
Small 2 year old plants that have grown for a single summer in soil might need a little extra care during their first winter outside. The following photographs will show you one way to do this successfully.
Older plants are less sensitive, but as described earlier, do not forget the same autumn and winter care. The buds that will give rise to next year’s shoots are at the soil surface and need to be covered with some fine gravel and possibly protected against heavy rain and excessive frost.