AOS Oncidium Alliance Culture Sheet

Oncidium Alliance

Warm-Growing Genera

This varied group of orchids includes plants from many types of environments. Some come from hot and dry areas, while others grow in less severe conditions. More specific instructions may be available from the grower. Some genera included are Aspasia, Brassia, warm-growing oncidiums and miltonias (often called the Brazilian-type), and many of their hybrids.

LIGHT can be from just bright to almost full direct sun depending on the plant. Most will thrive with one to several hours of sun a day. Generally thicker-leaved plants can stand more light, such as "mule-ear" and "equitant" oncidiums. In the home, east, south or west windows are ideal. Many types will grow under artificial light: four fluorescent tubes 6 to 12 inches over the plants are necessary for proper growth. Metal- halide and sodium-vapor bulbs also provide sufficient light without needing to be so close to the plant. In a greenhouse, 20% to 60% shade is required, or about 2,000 to 6,000 foot- candles, depending on the plants grown.

TEMPERATURES for this group are generally called intermediate to warm: 55 to 60 degrees F at night, and 80 to 85 degrees F during the day. Temperatures to 95 to 100 degrees F are tolerated if humidity and air movement are increased as the temperature increases.

WATER requirements vary with the type of plant. Generally, plants with large fleshy roots and/or leaves need less frequent watering than thin-leaved and/or thin-rooted plants. Watering should be thorough, and plants should dry at least halfway through the pot before watering again. This may be every 2 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 species have winter rest periods.

HUMIDITY should be between 30% and 60%. Most of these orchids require less humidity than some other orchids. In the home, placing the plants on trays above moist pebbles is ideal. Misting the plants in the morning may help increase humidity but is usually not recommended for fleshy-leaved types. Most greenhouses have adequate humidity.

FERTILIZER should be applied 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 other media or on slabs. If skies are cloudy, applications once a month are sufficient. Some growers use a high-phosphorus, 10-30-20 formulation bloom booster as plants approach blooming.

REPOT when new growth begins from the base of the plant, which is usually in the spring. A fine-grade potting medium is usually used with fine-rooted plants and coarser mixes with large-rooted plants; the standard size is medium-grade. Usually the lowest one-quarter to one-third of the pot is filled with drainage material, either crock shards, rocks, or Styrofoam "peanuts". The plant should be positioned in the pot so that the newest growth(s) are farthest away from the edge of the pot, allowing the maximum number of new growth before crowding the pot. Spread the roots over a cone of potting medium and fill in around the roots. Firm the medium well around the roots by applying pressure. Keep humidity high and the pot dry until new roots form. A vitamin B1 compound may help establish newly potted plants.

"Equitant" and "mule-ear" oncidiums, as well as other fleshy- leaved and/or large rooted plants, can be grown on slabs of cork bark or treefern or in pots of a coarse, well-drained medium such as charcoal.

Prepared by: Education Committee, American Orchid Society, 6000 S. Olive Ave., West Palm Beach, FL 33405 (407) 585-8666.