Oncidium orchids in the horticultural trade, is a genus that contains about 330 species of orchids from the subtribe Oncidiinae of the orchid family (Orchidaceae). It is distributed across much of South America, Central America, Mexico and the West Indies. Common names for plants in this genus include dancing-lady orchid and golden shower orchid.
This is one of the few orchids that actually thrives on a few hours of direct sunlight each day. Place the plant in an east or west facing window (preferable with a sheer or Venetian blind covering it) where it can soak up the sun’s indirect but abundant rays. Dark green leaves indicate inadequate light exposure.
Refrain from watering until potting mix is dry half way through. You can check this by feeling the medium approx. 1 inch down from the surface of the plant. This frequency could wind up being every other day (during growing season) to once a week or every two weeks (dormancy). Water Oncidium less during summer dormancy. Keep in mind that plump pseudo bulbs indicate a healthy, adequately watered plant, where shriveled bulbs indicate a need for more water.
Temperature: This group is classified as intermediate to warm, meaning that the plants can withstand 12°c at night and up to 30° in the day.
If plant is in bark (which is typical), use high-nitrogen (30-10-10) during growing season. Otherwise use a balanced fertilizer (20-20-20). That said: rather than fertilizing weekly as you would with Phalaenopsis, fertilize every other week in half-strength and make sure to flush the fertilizer with clear water once a month. Fertilize more during sunny conditions which lead to photosynthesis and more energy use by the plant. The bigger the plant, the more fertilizer needed.