Dividing and back bulb removal
If required, the plant may now be divided or have a few of its back bulbs removed. The back bulbs are the oldest and leafless bulbs which have discarded their foliage and have been supporting the younger bulbs and their new growths. These bulbs are of great benefit and should not be removed unless they outnumber the green bulbs in leaf. In this case the excess back bulbs become an encumbrance to the plant and should be removed to restore the balance of the plant. A plant which is growing in more than one direction, as indicated by the new growths, may be large enough for division into two plants if at least four bulbs, including both green and leafless bulbs, can be retained on each piece. The pseudo bulbs are joined together by a hard woody rhizome which is visible on Cattleyas, for example, but hidden on Cymbidiums and Odontoglossums. In the latter its position can be determined by gently pressing the bulbs apart. To divide a plant or remove an unwanted back bulb this rhizome must be cleanly severed with a sharp knife or pair of secateurs. As a general rule for most of the bulbous orchids, never reduce a plant or divide it to less than four good bulbs, otherwise it will be greatly weakened and will take several years to restore itself to flowering size. However, there are a few exceptions, such as the Pleiones, where the old bulb decomposes quickly and plants never consist of more than one green bulb each year.
For the bulbless orchids, if it is necessary to divide a very large Paphiopedilum, the rhizome should be severed between the growths leaving at least four growths on each division.
The old back bulbs removed from Cattleyas and Cymbidiums will start new growths if potted up singly, and if grown for several years will produce further flowering sized plants. However, whether one is prepared to give up space for several years to a non-flowering plant identical to one already flowering, is a matter of personal choice. In a greenhouse these plants can be grown to flowering size within three or four years, but indoors, they may take as long as six or seven years, during which time they require as much care and attention as flowering plants, but with less immediate reward to the grower.
Repotting
Having seen to the roots and bulbs, the prepared plant is now ready to be returned to its pot. Plastic pots are recommended for indoor orchids as they have many advantages over the old clay pots. They are cleaner and lighter to handle and do not absorb water; all the water given to the plant goes into the compost. The open bark mix required by orchids will dry out very quickly in a clay pot making it extremely difficult to keep sufficiently moist.
Not all plants will need a larger pot after repotting. Some, such as the Paphiopedilums, will require little if any root trimming and, after shaking off the old compost, they can be happily returned to their old pot. They rarely make sufficient roots to fill their pot as do other orchids. Plants which have been reduced in size by the removal of unwanted pseudo bulbs may well fit in the same size pot as before, and divisions will probably need smaller pots. The correct size is judged by placing the plant in the pot with the oldest bulbs against the rim. There should be just sufficient room in front of the plant for a further two years‘ growth before it will again reach the pot rim. If the container is considered too small then a larger one must be found, but it is a mistake to overpot and nothing looks worse than a small plant in an oversized pot surrounded by an expanse of compost. Overpotting also leads to overwatering, so be on the safe side and use as small a pot as possible, leaving just sufficient space as described.
Some form of drainage will be necessary at the bottom of the pot. This may be whatever is available to you, broken pot shards or broken polystyrene tiles make an ideal drainage. Just sufficient is required to cover the bottom of the pot. On top of the drainage crocking is placed a layer of compost. This layer should be deep enough to enable the plant to be placed so that the base of the leading growth is level with, or a fraction below, the rim of the pot. Some orchids have a tendency to grow upwards, each bulb being made slightly above the previous one. In this case it may be necessary to bury the oldest bulbs to bring the leading bulb into position. With its roots tucked underneath its bulbs the plant can be held in place with one hand, while compost is poured in with the other, until all the space is filled. It is important to work the compost in evenly all round the sides, particularly round the back, to ensure that there are no cavities left around the roots. The compost is then pressed down with the fingers; a potting stick is not necessary, and it should be possible to get the compost firm enough to hold the plant stable. When the pot is half full some growers like to add a pinch or two of bone meal or hoof and horn to act as a slow release fertiliser. If used, it should be restricted to a pinch, as harm can be done to new roots through burning if this is overdone. The compost should finish just below the rim of the pot to allow for future watering. For reference it is always a good idea to make a record of the potting date on the label, and whether the plant was dropped on or repotted.
Repotting bulbless orchids
Bulbless orchids such as Phalaenopsis and Paphiopedilums should be repotted in exactly the same way as orchids with bulbs although there will be little old material to be removed and very little trimming of the roots should be necessary. You may find that your Phalaenopsis plants have produced extensive aerial roots outside the pot. This is quite natural and it is a mistake to try and force these into the new pot. If compared with the roots inside the pot, it will be seen they are different in appearance and they will suffocate if buried. If any of them are dead or have become broken they should be shortened for the sake of appearance. This will not harm the plant which will very quickly make new ones. Repot the plant leaving the exposed roots outside the pot.
Care
The immediate after care of a newly potted plant is important. No matter how carefully you have handled the plant, the disturbance will have been a shock to its system. Nevertheless, repotting is beneficial to the plant and with the right attention it will soon respond by making new roots. For the first two days after repotting the plant is better left dry to allow any damage to the roots to heal and prevent any rot setting in. During this period the plant may be sprayed or the leaves wiped with a damp sponge to keep them fresh.
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