Information on Oncidiums
Oncidiums (on-SID-ee-um)were one of the first of the tropical epiphytic orchids introduced into Europe and still remain a popular genus of orchids among growers who wish to diversify their collection. Oncidiums contain a wide variation of plant form, size, shape, colours and size of flowers making them extremely interesting orchids to grow. Yellow and brown colours predominate. This large orchid genus of more than 750 known species is distributed from Florida to Argentina with the greatest concentration of species in Brazil and the mountains of Colombia, Ecuador and Peru. Oncidiums are mostly epiphytes ranging from sea level to elevations of approximately 4000 metres.
Cultivation: Oncidiums are generally regarded as being an adaptable group of orchids. The species from high in the Andes are cool growers while those from the lowlands are mostly intermediate growers. Those species with tall pear shaped pseudobulbs (such as Oncidium sphacelatum and Oncidium varicosum) are in continual growth and should be kept moist. Terete leaved species and those with very small or nearly round pseudobulbs should be allowed to dry out between waterings. A short dry period after flowering will actually promote stronger growth. Most species of Oncidiums are grown in pots. Composts should be well drained but retain some moisture. Bark mixes are suitable. Under potting is better than over potting. Some species suffer from root rot and will do better if grown on slabs. This will allow roots to dry out after watering. Air movement is important for these orchids which, as a general rule, do not require high humidity.
Light: They will tolerate moderate to bright light, but if the leaves begin to turn red then reduce the light intensity.
Repotting: This will be required when the potting mix has broken down or the plant has grown too large for the pot. All potting should be done just as new growth commences, usually in the spring. Plants should be divided into flowering size divisions of at least three back bulbs plus growths.
Fertilizers: A complete fertilizer should be applied regularly at a rate of about half the manufacturer’s recommendation.
Pests and Diseases: These orchids are subject to attack by the usual pests and diseases. Provided a reasonable standard of culture is maintained no particular problems should be experienced.
Temperature: Intermediate growing species are more suited to sub-tropical Queensland.
Oncidium sphacelatum is an ideal garden plant, and many fine specimen plants are grown in well-drained beds or hollow logs. Equitant types grow well, mostly on mounts, and make large plants, but if they start to deteriorate, death usually follows. The mule eared types such as Oncidium lanceanum and Oncidium splendidum also grow well in this area.
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