Cymbidiums are the most common orchids grown in Victoria. Their popularity is due mainly to the many colourful, long-lasting blooms that they produce but also to their ability to grow and flower under a wide range of conditions and to survive a degree of neglect that would kill most other orchids. However, some attention to cultural conditions is needed if you hope to grow and to flower your cymbidiums well. Regular watering and fertilising, effective pest control and, most importantly, exposure to the correct light level throughout the seasons, should lead to success. Care should also be taken to protect the flower spikes from damage during winter. They are badly damaged or even destroyed by hail, while exposure to frost causes the buds to blacken and fall before they open. Flowering plants and those in bud should therefore be moved to a sheltered spot, for example, a covered verandah or under the eaves on the north side of your house. While flowering plants may be moved indoors for short periods, lengthy periods indoors will retard growth and subsequent flowering.
Light and Air Movement. Cymbidiums are best grown in a situation where they receive about half the level of full sunlight for most of the year, full sunlight during winter. A shadehouse covered with shadecloth (nominal shade factor of 50%) is ideal, provided that it is not overshadowed by nearby trees. Plants will grow almost as well under heavier shade, but they will flower poorly. Cymbidiums will not flower well if placed beneath a tree that casts a heavy shadow. If possible, place the pots on a raised wire mesh bench to provide good air circulation and take care to protect the flowers from snails and slugs.
Watering and Fertilising. Providing that cymbidiums are grown in an open, free-draining potting mix, they can be watered on every sunny day between October and April. Less water is needed at other times, once weekly being sufficient in mid-winter. Liquid fertilisers can be applied at weekly intervals for most of the year. High-potassium fertilisers, such as Campbell’s A®, are recommended for use between August and the end of December and high-nitrogen fertilisers, such as Aquasol®, at other times. Slow-release fertilisers may also be added in October.
Repotting. Cymbidiums respond well to repotting every two to three years, even if they have not outgrown their container, because pinebark potting mixes decompose after that time, becoming acidic and interfering with free drainage. October and March are regarded as the best months in which to repot. Remove the plant from its pot -it may be necessary to cut the old pot if the plant has not been repotted for many years. Then remove all the old mix and any soft, dark, decaying roots. Repot in a commercial pine bark potting mix, using 5-10 mm particle size for small plants and 10-18 mm particle size for flowering sized plants. Hold the plant so that the bases of the pseudobulbs are about 25 mm below the rim of the pot and with the other hand till the pot with mix, working it between the roots. The final level of mix should just cover the lower quarter of the pseudobulbs. Add a slow-release fertiliser, such as Osmocote-Plus®, (a tablespoonful in a 200 mm-diameter pot is sufficient) and tap the pot until the granules make their way below the surface of the mix.
These cultural notes are kindly provided by the North East Melbourne Orchid Society. Details of when and where this and other OSCOV member societies meet each month may be found under the Members section of this website.