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Oncidium
Oncidium
on-sID-ee-um

This is an extraordinarily large and diverse New World genus with an equally diverse number of habitats. Oncidiums may originate anywhere from sea level in the tropics to the high elevations of the Andes. This obviously makes cultural generalizations difficult. Some genera included are Aspasia, Brassia, Ionopsis, warm-growing Miltonias and many other species.

Light
needs can vary from bright to nearly full direct sun depending on the species. Most will thrive with one to several hours of sun a day. Generally, thicker leaved plants, such as "muleear" and "equitant" oncidiums, can stand more light. In a greenhouse, 20 to 60 percent shade is required, or about 2,000 to 6,000 footcandles, depending on the plants. In the home, east, south or west windows are ideal.

Temperature
For this group are generally considered intermediate to warm: 55º to 60º F at night, and 80º to 85º F during the day. Temperatures up to 95º to 100º F are tolerated if humidity and air movement are increased as the temperatures rise, a good general rule in any case.

Water
requirements vary with the type of plant. Generally, plants with large fleshy roots or leaves need less-frequent watering than thin-leaved or thin-rooted plants. Watering should be thorough, and the medium should dry at least halfway through the pot before watering again, This may be every two to 10 days depending on weather, pot size and material, type of orchid and type of potting medium. Plants not actively growing should be watered less; many of species have winter rest periods.

Humidity
should be between 30 and 60 percent. Many Oncidiums require less humidity than other orchids. Most greenhouses have adequate humidity In the home, placing the plants above moist pebbles in trays is ideal.

Fertilize
regularly while plants are actively growing. Applications of 30-10-10 formulations twice a month are ideal for plants in a bark-based potting medium. A 20-20-20 formulation should be used on plants in other media or on slabs. If skies are cloudy, applications once a month are sufficient.

Potting
should be done when new growth is about one-half mature, which is usually in the spring. Fine-grade potting media are usually used with fine-rooted plants and coarser mixes with large-rooted plants; the standard size is medium grade. The plant should be positioned in the pot so that the newest growth is farthest away from the edge of the pot, allowing the maximum number of new growths before crowding the pot. Spread the roots over a cone of potting medium and fill in around the roots. Firm the medium around the roots. Keep humidity high and the potting medium dry until new roots form.
Oncidiums can be grown on slabs of cork bark or on peace of branch as well as in pots filled with a coarse, well-drained medium such as charcoal. This allows the drying between waterings that these types need.
 

  Books on Oncidium

What potting media are used at Kew (The Royal Orchid Collection) >>

how to grow multigenera Oncidiinae hybrids (the modern hybrids) >>

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