Oncidium Care Guide

Light

Oncidium light requirements can vary depending on the species, ranging from bright indirect light to nearly full direct sun. Most Oncidiums will grow well with one to several hours of sun each day. Thicker-leaved types, such as mule-ear and equitant Oncidiums, can usually tolerate higher light levels than thinner-leaved varieties.

In a greenhouse, around 20% to 60% shade is generally suitable, or approximately 2,000 to 6,000 foot-candles, depending on the plant. In the home, east, south, or west-facing windows are usually ideal. Many Oncidiums can also be grown under artificial lights. Fluorescent tubes, metal halide, or sodium-vapour lights can provide sufficient light when positioned appropriately.

Temperature

Oncidiums are generally intermediate to warm-growing orchids. They usually prefer night temperatures of around 13°C to 16°C and daytime temperatures of around 27°C to 29.5°C.

They can tolerate higher temperatures, up to around 35°C to 37°C, provided humidity and air movement are increased as temperatures rise. Good airflow is especially important in warmer conditions.

Watering

Watering requirements vary depending on the type of Oncidium. Plants with large, fleshy roots or thick leaves usually need less frequent watering than thin-leaved or fine-rooted types.

Water thoroughly, then allow the potting medium to dry at least halfway through the pot before watering again. Depending on the weather, pot size, pot material, orchid type, and potting mix, this may mean watering every two to ten days. Plants that are not actively growing should be watered less often, and many species require a drier winter rest period.

Humidity

Oncidiums generally prefer humidity between 30% and 60%. Many types need slightly less humidity than some other orchids, making them relatively adaptable.

In a greenhouse, humidity is often naturally sufficient. In the home, placing plants above trays of moist pebbles can help increase humidity around the plant without leaving the roots sitting in water.

Fertiliser

Fertilise Oncidiums regularly while they are actively growing. For plants grown in bark-based potting mixes, a 30-10-10 fertiliser applied twice a month is suitable. For plants grown in other media or mounted on slabs, a balanced 20-20-20 fertiliser is recommended.

During cloudy weather or periods of slower growth, fertilising once a month is usually sufficient. Avoid overfeeding plants that are not actively growing.

Potting

Oncidiums are best repotted when the new growth is about half mature, usually in spring. Fine-grade potting mixes are generally used for fine-rooted plants, while coarser mixes are better for larger-rooted types. Medium-grade potting mix is commonly suitable for many Oncidiums.

When potting, position the plant so that the newest growth is farthest from the edge of the pot. This gives the orchid room to produce new growths before becoming crowded. Spread the roots over a cone of potting medium, fill around the roots, and gently firm the mix into place.

After repotting, keep humidity high but allow the potting medium to remain fairly dry until new roots begin to form. Equitant and mule-ear Oncidiums, as well as other fleshy-leaved or large-rooted types, can also be grown mounted on cork bark or tree fern, or in pots with a coarse, well-drained medium such as charcoal. These conditions allow the roots to dry between waterings, which these types prefer.

Reference

Article adapted from the American Orchid Society culture sheet on Oncidium orchids.