Ponerorchis are potentially of great interest to the lover of our own native orchids since their requirements are similar to those that grow in our own mountainous habitats: a sunny to semi-shaded place with a moist atmosphere and plenty of good air circulation. However, Ponerorchis are, first of all, fascinating pot plants for the alpine house. During most of the autumn, winter, and again most of the spring, while dormant, no water is needed, but the air should be sufficiently moist. Temperatures during the peak of dormancy, in winter, should be around 0 to 5° C. Please consider that they grow in very loose soil and are covered with heavy snow during winter, therefore protection against frost is needed. In nature the plants usually bloom in July. Flowering in Japanese cultivation takes place in June.
Pots, Medium and Fertiliser
Ponerorchis develop only a very few and thick roots that like to grow vertically down into the soil: deep pots, not pans, with a large drainage hole are required. The plants like to grow in a very light and loose medium with perfect drainage. The Kanuma soil. Japanese use a fine grainy medium – “Kanuma soil”. It resembles coarse sand, but it is very porous and much lighter in weight. It consists of unburned miniature clay pebbles. This material is not easily available in western garden centres but if you wish to use it you may be able to obtain it from bonsai specialists. I have seen Kanuma listed by Herons nursery in Lingfield, Surrey, bonsai.co.uk and by bonsai-mart.co.uk, (more details on these should be sought via a search engine).
Kanuma is not essential and other media should be tested, trying different materials to optimise growth. The one essential point about cultivation however is GOOD DRAINAGE. The area where the shoot meets the tuber and from where the roots emerge, is susceptible to rotting if the compost is too wet or too heavy. It may seem trivial, but it can kill your plants. Do please ensure good drainage, even if it means growing the plants in nothing but drainage material such as unmixed Kanuma or Perlite.
We have used the following mix without fatalities (on the part of the plants), but further improvements might be required. The mix could consist of two parts crushed Seramis© (without the dust or the larger lumps), one part fine perlite, pumice or perlag (again, without the dust) and one part dark, loose coarse humus. Japanese growers recommend that this humus is NOT peat or beech / oak leafmould (as this decomposes too quickly). I suspect that fine orchid bark would do for the humus content, however Sphagnum moss is specifically recommended in Japan. The growing medium should be pH-neutral or very slightly acidic. It needs to be replaced for each new growing season to ensure that disease is not carried over and that the humus does not compact, clogging the required free drainage. To grow substantial tubers, bearing large flower trusses with lots of large blossoms, fertilisation is required. Japanese growers use a balanced organic slow-release fertiliser, which is placed on the soil surface and releases its nutrients during watering.
The Growing Season
Between the end of March and the middle of April newly purchased tubers should be planted, or older ones replanted. For a single tuber a deep pot of not more than 8cm wide is suitable, however plants probably look better if they are grown in small groups of one single cultivar, perhaps 3-5 in a 10-12cm pot. The tubers’ eyes, from which the growth originates, must be on top, and should be covered by about 1cm of substrate. Distance between tubers should also be about 1cm.
Once the temperature rises (slowly and gradually, as sudden increase will make the plants ‘shoot’) the growth will finally show up on the surface and slowly grow taller, unfold its leaves and later burst into flower. Flowering may last up to a month, after that the plants remain green until autumn. During the growing season the plants can withstand quite high temperatures, although this is not essential. High temperatures mean that high humidity must also be provided however. In autumn growth slows and leaves yellow and then all of the upper parts of the plant die back underground. The roots will eventually also die while the plant is getting ready for its long winter dormancy.
Watering should begin once the growth shows up on the soil surface, and fertilisation should start two or three weeks after. Both continue until shortly after the leaves have died, when the temperature gradually begins to fall to autumn levels. Between watering, the medium’s surface should be allowed to dry. During the months of dormancy plants must be kept cold, and no water should be given until the next spring. Alternatively tubers may be stored almost dry in dried Sphagnum moss in a domestic refrigerator, however these must be looked at regularly in case the moisture level in the Sphagnum is not right.
Aphids, snails and slugs are the greatest danger, and should be dealt with accordingly.
Text, content and pictures © P.J. Christian, BSc Phd 2015