Heritage Orchids

Cultivation - Pleiones

SUMMARY
Pleiones are a small group of cool and intermediate growing orchids, originating mostly from China, Northern India, Thailand and Nepal. Most grow naturally close to the snow line at the edges of woods and forests. They are semi epiphytic and can be found growing on moss covered tree branches or around the bases of trees and in leaf litter. Closely allied to Coelogyne, the flowers are large compared to the size of the plant, and they are delicately coloured. 

Pleiones have pseudobulbs of about an inch in diameter, more or less. The flowers develop from the base and the buds appear at the side of the pseudobulb. When flowering is over, the leaves develop, and they can be quite large, more than 6 inches long and 2 inches wide. These leaves feed the new bulb which develops during the growing season. When this is over, the leaves drop and it is time to give the plants a rest. At that time, the plants should have developed a new, fat and plump bulb ready for next year. The old shrivelled bulb should be removed, as it could cause problems by rotting, and the bulbs are either left in dry compost to over-winter or removed from their compost. In that case, the roots are trimmed to about 1/2 inch, the bulbs are cleaned and placed in a cool and frost free, dark, airy place until the new buds appear. Then they are potted and the cycle begins again.

In conclusion, Pleiones are very rewarding little orchids, they flower reliably once they reach flowering size, and many bulbs will produce two or even three flowers per bulb. They multiply easily and only take a couple of years to reach flowering size. Some even have a delicious scent. 

By choosing a number of different varieties, it is possible to have flowering pleiones for seven months of the year. Certainly worth a try ! 

DETAILED INSTRUCTIONS

TEMPERATURE
Most pleiones, especially spring flowering, are cool growing (minimum 3C/39F in winter). These may be kept in the fridge during winter.
Autumn/winter flowering ones (e.g. P. praecox and its hybrids) require slightly higher temperatures, minimum 5C/41F in winter.
P. maculata is a tropical pleione and needs to be grown warm (min 18C/65F in winter). If this is kept too cool, it may grow leaves but will never flower and multiply!!!

LIGHT
Pleiones enjoy good light, but they need to be protected from strong sun light from the beginning of March onwards, as their leaves are quite tender and easily scorched. Use shading if you grow them in a greenhouse; ensure they are not on a south facing window sill.

During the summer, all will benefit from a spell outdoors. When you put them out into the garden after flowering and there is no danger of frost, give them a little shade at first until they become acclimatised, then they can withstand a sunny aspect quite well as long as their feet are cool. If they are exposed to the full blast of the midday sun, a little shading can be beneficial.

WATERING
Pleiones like moist compost during the growing season which is between March/April and October. Both spring and autumn flowering varieties have the same growing cycle, the only difference being that the former flower at the beginning of the cycle and the latter at the end.

After the dry rest period, re-start watering when the first buds show. At this stage the plant have few roots, so water sparingly at first, increasing as growth gets under way. When the leaves develop, usually at the end of flowering, water every week or when the compost has become dry. Lift the pot to test its weight, if heavy, its wet; if light, its dry. Use clean, fresh water - rainwater if you have it.

In hot weather, pleiones enjoy an evening misting over the leaves. This raises the humidity, which is especially appreciated if they are grown in a greenhouse. Outdoors, humidity in the air rises in the evenings as temperatures drop, so the plants tend to look after themselves.

From October, reduce watering and when all the leaves have fallen, remove them and stop watering altogether. The bulbs must have a rest and be completely dry (see detailed explanations lower down). 

FEEDING
Pleiones are moderate feeders and all fertilisers should be diluted to about 1/4 strength of that indicated on the pack. A high nitrogen plant food can be applied from April to August. I switch between Seaweed Extract and Fish Emulsion at every other watering.

A foliar feed with Maxicrop is also appreciated. Use it at half recommended strength.

During late August / September, change to a higher potash feed, again at 1/4 strength. This will encourage the new bulbs to ripen in readiness for the rest period. Feeding should cease by October and no more should be given until the following spring, when the leaves are growing (about March). Then normal feeding can resume.

RE-POTTING
Pleiones should be re-potted every year in fresh compost. The bulbs must not be buried in the compost but should at most be one third submerged.  

Re-pot your pleiones when dormant; just after Christmas would be a good time. Please be careful when handling the pseudobulbs at this stage. If you damage the tiny flower shoot of the spring flowering kind, there won't be another one until the year after.

Question: Why should pleiones be re-potted when dormant ?
Answer:   It's safer that way. 

Let me explain. When a living pleione root is damaged, it will not dry and form a little stump at the point of damage like any other plant. Instead, the entire root will die right back to the bulb. A pleione has few roots, and losing one would  severely set it back. Therefore it is best to wait until dormancy when the roots have died naturally and no harm will come to the plant when roots are cut back.

We recommend leaving about 1/2 inch of dead root to serve as anchorage when the bulbs are re-potted.

Pots and Containers
Pleiones can be grown either one to three in a pot or more in a bowl. If planted singly in a pot, aim for a depth of no less than 9 cm, preferably 11 cm, to accommodate the roots during summer. A good root run aids the development of good sized replacement bulbs for next year. 

For groups of pleiones I use bowls, their diameters ranging from 15cm (will take 5 - 7 bulbs) to 30cm (up to 30 bulbs at a squeeze). Bulb bowls and cactus bowls are very presentable and they have holes in the bottom for drainage. I tend to use clear plastic mixing bowls (less expensive) with great success. They are just deep enough to give the plants a good root run. Holes must be drilled in the bottom to allow water to drain away. The clear plastic allows me to check on root development and the soundness of the compost. When I want to display a bowl, I just pop it into a pretty basket for the occasion.

Tip: Use pots that have two tier or side drainage. Bowls that have holes just in the bottom should be stood on gravel, pebbles, Hortag or similar so that water can drain away easily. Never allow pleiones to get water-logged, for the roots will rot and the plant will perish.

Summer Quarters
Pleiones prefer a cool root run. This can be difficult if the hot sun falls directly on small black plastic pots. Put your hand on the sunny side of a plastic pot in the summer, especially a black one, and you'll be amazed how hot it is. Not something a pleione would experience in its natural habitat, where it nestles among cooling mosses and lichens.

There are many ways one can prevent pots from overheating. I place my potted pleiones into a plunge during the growing season. This is simply a larger container with holes in the bottom and sides, or a raised bed, filled with the same compost, where the pots are submerged with just the rims sticking out. I find that during hot summers, a plunge ensures better and more even retention of moisture and a comfortable, cool temperature in the pots. 

Compost
The compost mix should provide good drainage yet retain sufficient moisture for the plants to thrive. This can be achieved in many different ways, using a variety of components. In essence, there are two types of compost mixes: largely organic and largely inorganic.

A) My current favourite mix (organic) is this, both components to be moist (not wet) before mixing, otherwise the sphagnum stays at the top and the bark falls to the bottom.

Parts by volume

Component Supplier

3

Medium Bark e.g. Melcourt Potting Bark, sifted through a 1/8" sieve to remove dust and fine particles Fargro
2 Sphagnum Moss, dead, moist, chopped into 1/2 inch pieces www.lbsgardendirect.com
1 Supercoarse Perlite (optional), washed to remove dust www.gardendirect.co.uk

B) My previous favourite was the largely inorganic compost below, but my latest growing experience shows that compost A) results in stronger growth. However compost B) is very suitable for most hardy orchids.

Parts by volume

Component Supplier

3

Seramis or 
Ultrasorb

www.gardendirect.co.uk
2 Supercoarse Perlite www.gardendirect.co.uk
2 Coarse Vermiculite www.gardendirect.co.uk
2 Sterilised fibrous loam e.g. John Innes No 1 Garden Centres
1 Fine Bark Orchid Nurseries

Or you could try equal parts of loam, sphagnum moss and medium grade orchid compost, but be careful not to over-water.

Notes on Compost preparation
All elements of your compost must be free of dust and fine particles. I sift the moss through a fine grade sieve and I wash the perlite. If this is not done, every time you water your plants, you will wash the dust to the bottom of the pot where it settles as a spongy layer, preventing drainage. As a result, the roots will sit in water and will gradually rot and so will the plant.
Wash the Perlite? why not sift it too? Because when you sift Perlite, it creates a big cloud of dust, which will settle in your lungs, not a good idea. Washing is easy: pour the perlite into a bucket, fill with water and stir. The water will turn white with dust. Pour it away, fill up again with fresh water and allow to settle. Then, when you need it, remove the perlite from the bucket using a kitchen sieve. More exchange of water will be needed as you get to the bottom of the bucket.

Notes on over-wintering: it is essential that the bulbs are kept dry during this period. Just to be clear what is meant by 'dry': 

  • humidity (water in the air) is not a problem 
    but 
  • moisture (water in the compost) certainly would be. Combined with cold temperatures - doom !

Therefore, if you grow your pleiones in a cold frame and you wish to leave them in their compost over winter, leave the lights on to keep out the rain, but leave them slightly open to allow air circulation.

When it gets really cold, you can close them for short periods and place some layers of newspapers, bubble wrap etc. over the plants to protect them from frost. Remember, your aim is to keep them above freezing, but they can survive a short cold spell if kept dry. Depending on your locality, a cold frame may not be an option, a frost-free greenhouse or similar place may be safer.

If taken out of the compost for over-wintering, trim the roots to about 1.5cm (1/2 inch) to aid stability when planted next spring. It is a good idea to soak the bulbs briefly in a solution of Spraying Oil to protect them from the false spider mite Brevipalpus oncidii.  Suitable oils can be obtained from Orchid Nurseries or Hydroponics Suppliers.

Store the bulbs in a box in a cool but frost free place. Check them occasionally to ensure they are not rotting. A good way to avoid this is to spray them with a fungicide. Cover the bulbs with a loose sheet of paper to keep them airy but retain some moisture.

Re-planting should commence when the new buds show as tiny shoots on the sides of bulbs, usually about February/March. 

PROPAGATION
Happy pleiones produce more than one replacement bulb, a large one that will flower next year and one or more smaller ones that need to grow a little more to flower. In addition, they produce numerous small bulbs (bulbils) around the base of the old bulb or around the 'scar' formed when the leaves fall. 

All of these should be potted up together in trays or community pots (not singly or they will feel very lonely). As we say, the big ones look after the little ones, meaning that if there is any uneven watering, the stronger, more developed plants will mop up the water and therefore the smaller ones with the less developed root systems will not suffer.

This is the compost I use for small, non-flowering bulbs and bulbils:

Parts by volume

Component Supplier

1

Medium Bark e.g. Melcourt Potting Bark, sifted through a 1/8" sieve to remove dust and fine particles Fargro
1 Fine Bark (sifted to remove dust) Fargro
2 Sphagnum Moss, dead, moist, chopped into 1/2 inch pieces www.lbsgardendirect.com
1 Supercoarse Perlite (optional), washed to remove dust www.gardendirect.co.uk

Bulbils should be flowering size by the third of fourth year after planting. Make sure you label them - it's so easy to forget...

Last Updated:  19/12/2016 09:47