| |
|
|
· Pests
Pleiones are very beautiful and rewarding orchids from mountainous areas of Asia. They are among the easiest of orchids to grow and propagate. Although often referred to as terrestrial orchids most are actually epiphytic or grow in the leaf litter around the base of trees rather that in soil. Most species and hybrids are Spring flowering but a few flower in Autumn.
Pleiones are cool growing orchids producing pseudobulbs that need a dry cold but frost free winter rest. They are sometimes referred to as windowsill orchids because they grow very well at normal room temperatures in good light but not in direct sunlight which are the conditions provided by a North facing windowsill. They can also be grown in an unheated greenhouse with some shading or even outdoors during the frost free months. They don’t like prolonged temperatures above 25 deg C and below 0 deg C they will die. They also don’t like being cold (0-10 deg C) and wet at the same time. They grow best in bright light but not direct sunlight. Misting, shading and air movement (fans) can be used to reduce temperatures during heat waves. When the leaves have detached in Autumn the pseudobulbs should be allowed to air dry in a cool place. Pseudobulbs and bulbils of Spring flowering species should be placed in paper (not plastic) bags and stored in a dry, dark and cold (but frost free) place until the new growth buds at the base show signs of growth the following Spring (keep checking from Jan onwards). Autumn flowering species do not go completely dormant need overwintering potted up and slightly moist at higher temperatures (approx 5 -10 deg C) and in natural periods of daylight/darkness.
Pleiones can be successfully grown in clay or plastic pots or other containers. Clay dries out more quickly so may not be best for windowsill cultivation. Some prefer shallow pans or bowls rather than deeper pots. On windowsill's it’s usually best to place pots on trays of gravel to assist drainage and prevent containers sitting in water. In the cool greenhouse a sand plunge is best to keep the roots cool.
The medium must be very free draining with high air filled porosity (AFP) yet retaining good water holding capacity (WHC). These two properties may appear to conflict but don’t really. The aim is to create a fairly coarse medium which does not hold any free water between the particles but in which the particles themselves absorb and hold water. The spaces between particles must be full of nothing but air. Remember we are trying to make a medium more suited to epiphyte's than terrestrials. Recommended Pleione mixes usually contain various ratios of bark, moss, perlite, peat, vermiculite, charcoal, grit and even loam. Bark is normally the main ingredient. Some growers are strong advocates of moss as a major ingredient. I now avoid using moss because it tends to gradually compress and break down resulting in a rather spongy soggy mess with increased WHC and reduced AFP. I avoid peat and vermiculite for similar reasons. Following years of experimentation I now use only medium grade potting bark (5 parts) and perlite (2 parts). I even sieve the bark before use to remove all fines. For flowering size pseudobulbs this mixture has just enough WHC provided you don’t leave too long between waterings. It is almost impossible to over-water if pots are positioned on trays of gravel or in/on a bed of sand. When propagating bulbils or very small pseudobulbs I use finer grades of bark that I produce myself by sieving potting grade bark through a range of sieves or Melcourt propagating bark. Most species should be planted with one third protruding above the medium. A few species and hybrids do better if planted a bit deeper but it is not critical. Before planting remove any old tunic and trim back the old roots. It is helpful to leave approximately a quarter of an inch of the old roots to anchor the pseudobulb in the medium and prevent the pseudobulb being pushed out as new roots grow.
In early season the medium should be barely moist. Until the new roots grow there is no way the pseudobulb can take up water or nutrients. The medium should be kept just moist enough to prevent dessication. New roots don’t usually grow until the flowers start to fade. As new roots form begin to increase watering very sparingly until the new leaf grows. Do not start feeding yet. Once the new leaf is fully formed you can increase watering substantially and begin feeding with a weak balanced feed. Professional growers will feed with higher nitrogen in early season, balanced feed mid season and changing to a higher potassium feed in late season. A good balanced feed fed very dilute but often will give equally good results as plants have the capacity to store excess nutrients and use them when needed. During cold weather periods reduce watering and stop feeding. During periods of very warm weather water more often but be careful to maintain perfect drainage. Misting helps to cool the foliage. Pleiones are not fussy about water quality but if your mains water is very hard or smells strongly of chlorine it would be advisable to use rain water or softened water. Reduce watering when foliage begins to turn yellow in Autumn (Sept/Oct) and cease watering completely as the leaves go brown or fall off. Allow the new pseudobulbs to dry completely before separating from the old withered pseudobulb for winter storage. Don’t forget to harvest any bulbils from the old pseudobulb at the same time and look for any that have already fallen off.
Well fed plants will produce two or three new pseudobulbs each year from every one planted which is a very rewarding rate of increase. One pseudobulb can generate a potfull in just a few years. Many pseudobulbs also produce bulbils at the old leaf point which can be grown on to produce flowering size pseudobulbs in about three years. Some experts say that bulbils grow best when grown with mature pseudobulbs. This is probably because it is quite difficult to keep a pot or tray of bulbils at the correct moisture level because they are planted so shallow. Pleiones can also be propagated from seed using in vitro techniques. This is described fully in another section.
The only pest of any significance is a parasitic species of mite (Brevipalpus oncidii) which is microscopic and therefore difficult to spot without a strong lens. It gradually weakens the plants over several seasons resulting in smaller and fewer pseudobulbs, poorer growth, greater susceptibility to rot and a much reduced rate of increase. It is easy to cure with certain insecticides or spraying oil which should be applied to the plants during growth and to all pseudobulbs in winter storage. I routinely dip pseudobulbs in spraying oil at the start of the winter rest, before planting in spring and spray during growth. You should also keep a constant lookout for aphids when in leaf as these are vectors of viruses. Aphids should be sprayed and any virus infected plants should be burnt. Fungal infections of leaves are rare but I routinely spray with fungicide anyway just to be sure. Small areas of rot in pseudobulbs can be cut out and treated with fungicide or sulphur powder. Click here for cultivation supplies
|
.......................
|
© Copyright Koolplants, 2008. All Rights Reserved.