Requirements vary with the type of plant. Usually, plants with large, fleshy roots or leaves need less-frequent watering than thin-leafed or thin-rooted plants. Watering should be thorough, and the medium should almost dry out before watering again. This is dependent on the weather, type of orchid, pot, and medium used. Plants not actively growing require less water. Some types have a winter rest period and need less water. In the home. Place potted orchids on a tray of wet pebbles to keep the humidity constant. Humidity should run about 40% to 60%.
Light needs can vary from bright to nearly full direct sun depending on the species. Usually, thicker-leaved plants, such as "mule ear" and "equitant" oncidiums, can take more light. A screened patio is a good place to grow your oncidiums. In the greenhouse, 20% to 60% shade is required. They can be grown by a south, east, or west window with sufficient light.
Fertilize regularly while plants are actively growing. Orchids potted in a bark-based medium need a 30-10-10 formulation. Feed orchids mounted on slabs or other media a balanced 20-20-20 formulation every other week during warm weather. Reduce frequency to once a month during winter or cooler temperatures. A bloom booster like 10-30-20 just before blooming will give stronger, more numerous flowers.
Springtime is the best time to repot or mount your oncidiums. Usually, fine-rooted orchids take a fine grade potting mixture of tree fern, charcoal, and bark. Coarser mixes do well for large-rooted plants. Pot with new plant growth closest to the center of the pot. This allows maximum number of new growths before crowding the pot. Keep humidity high and potting medium dry until new roots have formed. Equitant and mule-ear oncidiums as well as other fleshy-leaved or large-rooted plants can be mounted on a tree fern plaque or cork bark. This allows drying as needed.