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Growing Oncidium Orchids

Light
Oncidiums need bright light to nearly full direct sun depending on the species. Most will thrive with one to several hours of sun a day. East, south or west facing windows are all suitable positions. Many types of Oncidiums will also grow under artificial light. The leaves should be bright green as opposed to dark green or reddish green. Reddish green indicates too much light and dark green too little light.

Temperatures
Oncidiums are generally considered intermediate to warm orchids. They require a minimum temperature ranging from 55-60°F (13-16°C) at night to 80-85°F (26-30°C) during the day. Temperatures up to 95-100°F (35-37°C) are tolerated if humidity and air movement are increased as the temperatures rise.

Water
During the growing season, water every few days, but allow the compost to dry out a little between watering. Reduce watering during the winter months to once a month or less. Oncidiums can withstand drought thanks to their large pseudobulbs which act as stores. Wrinkled pseudobulbs generally indicate a lack of water. Avoid overwatering as Oncidiums are prone to rot. Plants not actively growing should be watered less. Many Oncidium species have winter rest periods.

Humidity
Oncidiums enjoy moist air, requiring a minimum of 30-60% humidity. In the home, placing the plants in a tray of damp pebbles is ideal. In addition, mist the plants.

Fertilization
Fertilize regularly during the growing season. 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. The roots of oncidiums are particularly susceptible to fertilizer burn, so never use a full-strength mix.

Potting
Repotting should be done when either the medium decomposes or the pot becomes too small. Oncidium orchids like to be slightly tight in their pots in a very free-draining bark-based potting media. They 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. Keep humidity high and the potting medium dry until new roots form.

Propagation
Many of the oncidiums will form large clumps of pseudobulbs and develop into large plants. They can be easily divided into clumps in spring. Make sure you have at least three pseudobulbs in each division.

Pests and diseases 
Oncidiums are generally disease free. Keep an eye out for aphids, glasshouse red spider mite and mealybugs.

Tip for reblooming

If a plant is large and healthy but does not produce flowers in a reasonable time, then move your plant to a brighter location or a location that gets an hour or two of early morning sun.

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