| POTTING
Potting Epiphytes (Cattleyas, Dendrobiums, Oncidiums, Phalaenopsis, Vandaceous) Orchid potting is the subject of much debate and conjecture and each grower has a preference. In the eighties, commercial growers used rockwool based composts although looking back it is hard to work out why. It was awful stuff. Nowadays, "orchid composts" are still available in garden centres and nurseries and these are made up of all kinds of strange materials such as plastic chips and polystyrene. The best compost is one that closely resembles the natural conditions that the plant would grow in. Many plants are hybrids but their growing habits still resemble those of the original species from which they are derived. Most tropical orchids are tree dwellers. They are not parasites as they don't obtain any nutrient or moisture from the tree, they just use the branches as a place to cling to where they receive humidity, shade and pollinating insects. 
These are known as epiphytes. Their roots are thick (up to a pencils
thickness) and are capable of adhering to branches while at the same time
they are modified to obtain water from the atmosphere and that which
collects on the bark of the tree. So we need to mimic these conditions in
order to best satisfy these types of plant. This is why many plants like
to grow on pieces of bark that are hung up. But we also have to be able to
sensibly accommodate the plant and plants growing on bark dry out more
quickly so need more water and humidity to grow well. Their roots are open
to the atmosphere and drying breezes and spraying water around indoors
twice daily would be rather impractical.
A good compromise is needed and this comes in the form of a material that the roots can cling to that can be containerised for practicality and convenience. Ordinary plant pots are the natural choice. They can be either plastic or clay and are easy for us to move around and the plants can then be kept on benches or windowsills without the need for hanging. Clay pots have the ability to absorb moisture and their surface mimics that of a tree, especially if the pot surface is rough finished. Plastic pots also have an advantage in they don't absorb moisture so the excess slowly evaporates creating humidity around the roots. So pots are fortunately a good container in themselves so all we really need add is a little more material for the roots to anchor to and to support freshly potted plants. A traditional soil or peat based compost would not be suitable as this would clog the roots and hold too much moisture, causing the thick roots to rot. This would be fine for orchids that grow on the ground (terrestrials) but not epiphytes. What is needed is something that again resembles the tree branch and that doesn't retain an excess of water. Several options are available and the most popular three are: charcoal, brick and bark. CHARCOAL AND BRICK Lumpwood charcoal is a natural choice since it is a tree branch already, albeit in a different form. The burning process results in a material that is stable, porous, clean and pest free. It just needs to be washed and then becomes clean to touch and can be broken up into pieces of different sizes that are suitable for different sized plants. Charcoal also varies in texture and thickness so provides a perfect surface for the roots to grow over. It holds a little moisture but does not get sodden. It is an ideal potting material and it can easily be purchased from garages and DIY stores. Charcoal chunks are good but don't use the dust and very small pieces as these will block the drainage hole and cause waterlogging. Charcoal has one slight disadvantage: It is very lightweight. Top heavy plants (esp. Dendrobiums and Oncidiums) need a strong anchor and sometimes charcoal is not enough. There are two solutions. One is to use wider, shorter pots, especially those made of clay and the other is to incorporate some weight. A good choice for added weight is broken brick. Again, broken bricks are easily obtained and provide a good, clean surface for the roots. A mixture of broken brick alone is often used and this is a good mixture although it does dry out a little more quickly than a brick and charcoal mixture. When buying charcoal for potting, ensure that LUMPWOOD charcoal is used and not briquettes and also avoid charcoal pre-treated with lighting fluids. BARK Bark mixtures are the most popular potting mediums in use today. They are used by commercial growers and hobbyists alike. Bark is readily available, easy to handle and can be purchased in various grades from fine to coarse. If quality bark can be obtained it makes a good compost. It is relatively inert and takes years to break down. It can also be mixed with broken brick or broken charcoal. It is lightweight like charcoal so some weight is often needed but brick chunks will suffice. However, bark has one big drawback. Bark used to be unpopular. It was sold for decorative use in gardens and for orchid growing. However, it has become a hugely popular material for garden landscaping and as a result the amount of quality bark has dwindled. Cheap, inferior scrapings and shavings are commonly sold now and getting good quality bark is becoming increasingly difficult. Lots of the "bark" sold in DIY centres is long and thin pine shavings and they are slimy, matted together and mite infested. It quickly rots and can make the compost turn sour after a couple of years. But this can all be avoided if a better quality bark is sought. It may take some hunting down but at most DIY stores there is almost always a split bag which enables an inspection! The best bark is chunky and variable in size. This should then be soaked for a few days to remove bugs. It can then be mixed with fifty percent charcoal and some broken brick. The charcoal will prevent the souring of the mixture and the bark holds more moisture than charcoal which can be advantageous for maintaining humidity. Care must be taken to avoid excess water. Bark on its own is fine, as long as the chunks are large enough. It should be graded by hand to ensure the best bits are used. If good bark can be obtained then it makes a good mixture, especially when combined with charcoal. POTTING THE PLANT Potting is an easy process but a few steps must be taken to ensure that it is done correctly. Whether you use clay or plastic, full height or shallow pots, bark, charcoal or brick, or a combination, the procedure is still the same. Firstly, select the right size of pot for the plant. Orchids like to have crowded roots. Many actually need to be pot bound to flower well. Seedling sized plants that are growing rapidly may need an annual repot but most plants and certainly those that are mature, flowering size plants need only be re-potted every three years or so and maybe even longer if desired. So the pot shouldn"t be too large but it must be big enough to accommodate what might be a top heavy plant without the plant constantly falling over. Put a layer of large, random chunks of broken brick in the bottom, and then top up with broken charcoal and smaller brick pieces till about half full. Next, a small stick or green cane should be added, (with the exception of young Phalaenopsis) and this cane should be pushed fully into the mixture so that it is firm. If perforated "orchid pots" are being used then the cane can be secured by garden wire wrapped around the holes. If one cane alone is not particularly firm then add more to the outside edges of the pot and they can be drawn together and tied at the top like a "wigwam". The support should always be added BEFORE the plant is introduced. If potting on an established plant then the old potting material should be completely removed. Unlike potting a normal terrestrial plant, where new compost is added to the outside of the old, with epiphytes all old material is removed. Now that the plant is "BARE ROOT" the roots can be inspected. Dark brown roots are those which are dead and this is quite normal. These should be trimmed away. Healthy roots are usually grey or white in colour and those with green tips are actively growing. The plant should be potted with the oldest growth at the edge of the pot and the newest growth in the middle. Many plants grow new bulbs and canes in one direction and this should be catered for by giving the new growth room in the pot (not applicable to Phalaenopsis and Vandaceous which grow upwards). If the "direction" of growth cannot be determined then don't worry as its not critical but it may mean that the plant has to be re-potted sooner in the future. Most plants have young shoots coming out of one side which indicates the lead growth and Dendrobium canes get progressively larger as they grow so the longest cane should be in the centre of the pot. The commonest mistake is to put the base of the plant into the mixture. To avoid this, the plant should be tied to the wire / cane(s) with string or soft wire and secured so that the base of the plant is level or just below the rim of the pot. Then top up the pot with potting mix (charcoal, bark, brick etc) so that the roots are carefully covered but the base of the plant (and new, short roots) are ABOVE the mixture. As the new roots grow, they will grow DOWN into the mixture. If the plant is not secure, don"t be tempted to bury the base of the plant to keep it steady. If this does happen, the support must be altered, not the depth of the plant. Place the plant in its growing position and water in well. |
