Orchid growers often need to attend to an orchid that is old, pot-bound or shows signs of decline. Previous re-potting may have been neglected or the plant, having been recently acquired at an orchid auction, nursery or as a gift, is in poor condition. Damage to the plant by frost, sunburn, insect bites or various rots and fungal attacks may also require remedial action. Signs that an orchid requires attention include weak and straggly growth, moss on the surface of the mix, dieback, rot and poor flowering.
Plants that have overgrown their pots may also need attention. However, first assess whether you wish to keep the plant, as space and resources are scarce and your effort may be better spent on other plants. Typically, friends and relatives may have unknowingly donated diseased plants, more often than not cymbidiums that have belonged to the family for some time. It is probably in the best interests of your collection to discard such family heirlooms. Re-potting requires the complete removal of the old orchid mix and replacement with new mix in a new or sterilized pot of an appropriate size. Any dead portions of plant should be removed with sterilized secateurs and the plant sprayed for pests such as scale. The re-potted plant should also have some long-life fertilizer scratched in around the edge of the pot, and then watered well and placed in a protected area off the ground to re-establish.
Highly valued plants that would be difficult and/or costly to replace present a greater challenge. In many cases only a small part of the plant may survive, perhaps a single pseudobulb, cane or growth. For cymbidiums and other orchids with bulbs, cleaning up the back-bulb and placing it with fresh sphagnum moss in an inflated plastic bag, offers a good chance of new growth being generated. Some genera, such as lycastes, will often produce a new growth only if two or more joined pseudobulbs are used. Orchids with bare canes (e.g. dendrobiums), a creeping growth habit (e.g. bulbophyllums) or ones with no roots (all genera) are best tackled during the growing season (spring-summer-early autumn). The best option is to find a piece of the plant with a leading growth, as this is the most vigorous. However leafless canes, as is the case with many dendrobiums, may be all that is left to work with. If so, the canes can be cleaned and cut into sections containing two or three nodes. Each section should then be placed horizontally on a bed of live sphagnum moss and pinned down with small pieces of bent wire. It may take some time for the nodes to produce new growths.
Orchids with a creeping growth habit, such as bulbophyllums and epidendrums, should be restarted by attachment to a mount. Placing fresh sphagnum moss around (but not under) the growth helps to retain moisture and allows the emerging roots to attach themselves to the mount. Both the growth and surrounding moss should be fastened firmly to the mount with twisty-tie, and the plant then regular misted, especially during hot, dry weather. Root loss is a serious problem and paphiopedilums are among those orchids that can lose all their roots. I have had best results re-planting these plants in fresh sphagnum moss in a small pot. Secure the plant with a small wooden skewer to avoid movement and place it in a sheltered, shady position to recover. Once again patience is required as it can take many months for some paphiopedilum plants to re-grow roots, if ever!
Finally, how do you rejuvenate plants devastated by rot or fungal attack? The rot may move so quickly that the whole plant is at risk and remedial action is required without delay. The affected section of plant should be removed with a sterilized knife, razor blade or scissors and appropriate fungicidal sprays or sealants then applied to minimize further outbreak.