The Oncidium family is very large and includes many flower varieties. The most common flower variety is often referred to as the "dancing lady". This information is for Oncidium types that have thin leaves, pseudobulbs, and branching sprays of flowers.
Water: Oncidiums generally like to dry out between waterings. Adjust watering schedule to the time of year; in summer plants may need to be watered twice per week, in the spring and fall once to twice per week and in winter reduce waterings to once a week or less. Always water in the morning and try to avoid watering on overcast or rainy days. If the pot feels heavy or the medium feels damp, wait a few days before watering again. Do not use softened water.
Fertilizer: Fertilize with Dyna-Gro ‘Orchid Pro’ (urea free fertilizer is best) at the rate of 1/4 tsp. per gallon. Feed every other watering during the summer, and every third watering in winter.
Light: Grow in bright diffused light; east or west windows are ideal. South windows will work but one should be careful of the brilliant sun that will come in during the fall through spring months.
Temperature: Ideal night temperatures (fall, winter, and spring months) are 60 - 64 °F. Ideal daytime temperatures are 70 - 85 °F. Summer temperatures are generally a few degrees warmer. Temperatures above 95 °F can be tolerated for short periods of time with increased humidity and air flow (fans).
Humidity: Humidity levels for these plants should be kept at 40% or above.
Flowering: Flowering season can be at any time of year, but is generally heaviest in the fall and spring. Many hybrids can bloom 2-3 times per year. In order to initiate the flower spikes, it is important to grow the plant in an area where the night temperatures fall below 65 °F. Usually plants growing by a window are a couple of degrees cooler than the rest of the house. Keep a close eye on the spike (when it begins to produce flower buds) for aphids, and if they, or any other orchid pest appears, apply a spray of UltraFine Horticultural Oil.
Repotting: Repot every 1 to 2 years as the potting mix breaks down or as the plant outgrows the pot. (best done or taught be an orchid expert). For the hot and humid Washington DC area, try potting is in sphagnum moss in a clay pot. Oncidium like to be cooler, and this combination offers them happy cool roots!