Pleiones are a genus, comprising of approximately twenty species, of near-hardy terrestrial orchids. Their natural distribution extends from the Himalayas in central Nepal eastwards through the mountainous regions of central and southern China and it's neighbouring south east Asian countries, to Taiwan. They grow in a wide variety of habitats ranging from moss-covered rocks and tree branches to open ground and rock faces. The genus is often known as "Indian Crocus" or &"Windowsill Orchid". The latter is a very apt description as their cultivation requirements are very minimal. Thus making them an ideal subject for growing in the home, cold frame, or cool glasshouses. Their popularity has increased in recent years amongst both amateur and professional growers, and this has resulted in the breeding of many fine new hybrids. The majority of Pleiones are spring-flowering and the following cultivation notes are intended for these. Autumn-flowering species require slightly different treatment, as these do not go completely dormant during the winter months.
The composition of this is not critical but it should be well-drained and open, yet have the ability to retain some moisture. A combination from quite a large selection of readily available materials, either traditional or modern, may be used. These can include :- small-chipped Forest Bark, composted Forest Bark, coarse Perlite, medium-grade Pumice, chopped-live Sphagnum Moss or Ground Moss, Coir, Leaf Mould, Pine or Spruce Needles. The addition of a small quantity of ¼" (6mm) sieved Charcoal can be beneficial. The nutritional value of the compost mix is not an important consideration providing that adequate liquid feeding is carried out during the growing season.
Clay or plastic containers may be used with equal success. However, the latter should have extra holes drilled inthe base to improve drainage. Pans or half pots are preferable to standard pots as Pleiones prefer a shallow compost depth. The containers should be at least one third filled with drainage material such as "crocks", gravel or coarse pumice. Do not over firm the compost as watering will gradually settle it to a natural firmness. Most species and varieties require the pseudo- bulbs to be seated into the compost surface to approximately one-third of the bulb depth only. On commencement of growth the new roots will soon anchor the pseudo-bulb firmly in position. Exceptions to this rule include P.speciosa which needs to be almost buried and P.bulbocodioides which should be planted approximately two centimetres deep.
Once growth has commenced theplants should be moved from winter storage to a frost-free, but cool, environment. It is advisable to avoid direct sunlight at this stage since flower quality can be impaired. Very dry pots should be well watered initially by soaking from below;subsequent watering should ideally maintain the compost barely moist. This is to encourage the roots to search for moisture and consequently develop a stronger system. Flowering, which precedes leaf development, occurs in most species and varieties during March and April. As leaf growth develops, following flowering,gradually increase the supply of water, but at no time should the compost be sodden. Feeding with a liquid fertilizer should commence on a regular basis. Additional warmth and sunlight are now beneficial, but direct sunlight should still be avoided. A light overhead spray with water on a warm evening is much appreciated by the plants, as is adequate ventilation and circulation.
Towards the end of June when the leaves are fully developed, the plants may be moved to an outdoor situation. Early morning or late afternoon sun is not harmful, but some protection from the strong midday sun should be provided. Continue regular feeding and watering as required until mid-September.
As the leaves yellow and die back, watering should be reduced. A return to the cool glasshouse environment and weak sunlight help to ripen the new pseudo-bulbs which have formed at the base of the leaf. Care should be taken to afford protection against early frosts while the plants are still in leaf.
Dead leaves should be removed, the pot generally tidied and the compost allowed to dry completely. Store the dormant pseudo-bulbs in an unheated garage or shed, keeping the pots completely dry; light is not essential. Chilling during this period is not harmful; most species will withstand slight sub-zero temperatures whilst dormant.
Each flowering sized pseudo-bulb produces on average, two new ones each year. Although these may be divided off and potted individually, annual repotting is not necessary unless there is a danger of overcrowding in the containers. If this situation arises the quality of new pseudo-bulbs and subsequent flowering will be adversely affected. Any repotting required should be carried out during January before growth commences, as damage to the young shoots can be fatal to the plant. As the old pseudo-bulb shrivels and dies, bulbils are often produced on the top of it. These may be removed and potted also to increase stock, but it will take two to three years for these to achieve flowering size.