8/12/2019 Orchid Oncidium

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LIGHT needs can vary from bright tonearly full direct sun depending on thespecies. Most will thrive with one to sever-

al hours of sun a day. Generally, thicker-leaved plants, such asmule-ear andequitant oncidiums, can stand more light.In a greenhouse, 20 to 60 percent shade isrequired, or about 2,000 to 6,000 foot-candles, depending on the plants. In thehome, east, south or west windows are ideal.Many types of oncidiums will grow underartificial light: Four fluorescent tubes sup-plemented with incandescent bulbs andplaced 6 to 12 inches over the plants arenecessary for proper growth. Metal-halideand sodium-vapor bulbs also provide suffi-cient light without needing to be so closeto the plants.

TEMPERATURES for this group aregenerally considered intermediate to warm:55 to 60 F at night, and 80 to 85 F duringthe day. Temperatures up to 95 to 100 F aretolerated if humidity and air movement areincreased as the temperatures rise, a goodgeneral rule in any case.

WATER requirements vary with the type

of plant. Generally, plants with large fleshyroots or leaves need less-frequent wateringthan thin-leaved or thin-rooted plants.Watering should be thorough, and the med-ium should dry at least halfway through thepot before watering again. This may beevery two to 10 days depending on weather,pot size and material, type of orchid andtype of potting medium. Plants not activelygrowing should be watered less; manyspecies have winter rest periods.

HUMIDITY should be between 30 and60 percent. Many oncidiums require lesshumidity than other orchids. Most green-

houses have adequate humidity. In thehome, placing the plants above moist peb-bles in trays is ideal.

FERTIL IZE regularly while plants areactively growing. Applications of 30-10-10formulations twice a month are ideal forplants in a bark-based potting medium. A20-20-20 formulation should be used onplants in other media or on slabs. If skiesare cloudy, applications once a month aresufficient.

POTTING should be done when newgrowth is about one-half mature, which isusually in the spring. Fine-grade pottingmedia are usually used with fine-rootedplants and coarser mixes with large-rootedplants; the standard size is medium grade.

The plant should be positioned in the potso that the newest growth is farthest awayfrom the edge of the pot, allowing themaximum number of new growths beforecrowding the pot. Spread the roots over acone of potting medium and fill in around

the roots. Firm the medium around theroots. Keep humidity high and the pottingmedium dry until new roots form.

Equitant and mule-ear oncidiums, as wellas other fleshy-leaved or large-rootedplants, can be grown on slabs of cork barkor tree fern or in pots filled with a coarse,well-drained medium such as charcoal.

This allows the drying between wateringsthat these types need.

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Orchidand theAOS Orchi d Source Directory, 10 percent discount on items purchased througThe AOS BookShop and Orchid Emporium,and free admission to the International OrchidCenter in Delray Beach, Florida.

American Orchid Society16700 AOS LaneDelray Beach, Florida 33446-4351Tel 561-404-2000 Fax 561-404-2100E-mail TheAOS@aos.orgWeb site orchidweb.org

Oncidiumon-SID-ee-um

This is an extraordinarily large and diverse New World genus with an equallydiverse number of habitats. Oncidiums may originate anywhere from sea levelin the tropics to the high elevations of the Andes. This obviously makes cultural

generalizations difficult. More specific instructions may be available from the

grower. Some genera included areAspasia, Brassia, warm-growing miltonias

(often called the Brazilian type) and many of their hybrids.

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