The oncidium family is very large and includes many varieties such as the mule eared, equitant, rat tailed, and other varieties. This instruction sheet deals with oncidium types that have thin leaves, pseudobulbs, and branching sprays with flowers colored in yellow and mahogany.
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. If you have mini blinds or sheer curtains, you can break the light so that it is more diffused.
Ideal night temperatures (fall, winter, and spring months) are 60 degrees to 64 degrees. Ideal daytime temperatures are 70 degrees to 85 degrees.
Humidity levels for these plants should be kept at 40% or above.
Water when the mix just approaches dryness in large pots 6 inches or larger. This will mean about every 5-7 days. You can check the mix for moisture by sticking a wooden pencil into the mix about 3 inches-4 inches. When you pull the pencil out, check the wooden end. If it has turned dark in color, the mix is still wet and you should wait a day or two.
Fertilize with a higher nitrogen fertilizer such as 30-10-10 or 20-10-20. Feed every third watering year round.
Depending on the variety, the 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 degrees. Usually plants growing by a window are a couple of degrees cooler than the rest of the house.
Repot every 1 to 2 years as the mix breaks down or the plant outgrows the pot. Plants potted in a bark mixture should be carefully pulled out of the pot. Clean off the roots of the old mix, being careful not to break the good roots. Roots that are bad and should be cut off are those that are brown and mushy or papery. Those roots which are white or tan and are firm to the touch should be left alone. Simply place the plant into a new pot placing the oldest growth towards the back of the pot so there is room for the newer growths to develop for about 1-2 years. Oncidiums can be divided when there are 6 or more pseudobulbs. Divide, leaving 3 growths per each division.