Oncidium Culture Sheet
How to grow Oncidium orchids.
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Oncidium orchids can vary in the light they need to grow and flower, ranging from medium light to very bright. Avoid direct sun.
Window: Place oncidiums in a bright east, west, or south window, but watch for signs of developing sunburn. This will appear initially as a yellowing or tan patch facing the source of light. A sheer curtain can be used to protect from sun damage.
Artificial light: High-pressure sodium lights, fluorescent and compact fluorescent lights, and LED lights can all be used to grow oncidium orchids. Place high-light orchids closer to the middle of the growing bench, and move plants with lower light requirements closer to the ends.
Outdoors: Like most orchids, oncidiums benefit from being moved outdoors after nighttime temperatures remain above 60 degrees. Plants may need to be acclimated gradually to brighter conditions, and should be kept out of hot sun.
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Oncidium orchids thrive in intermediate to warm temperatures, and are not tolerant of prolonged dips into the 50s and 60s Fahrenheit. A combination of bright light and excessive heat may result in sunburn, which will appear initially as a patch of yellow, tan, or white discoloration, fading to light tan and forming a dry patch. Check plants regularly for sunburn.
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Oncidiums, being orchids with thin roots, are intolerant of fully drying out. Oncidium orchids want to be watered very heavily on watering day, and should dry about halfway through the pot before being watered again. Oncidium roots will rot if kept in standing water, or if suffocated by wet media, or if allowed to dry completely for a prolonged period of time. To water at a sink, run a tap of room temperature water, and hold the pot in the water, moving it so that the entire pot is thoroughly flushed with water to thoroughly drench the medium. Allow the pot to drain, and place back into the growing area. This is an ideal time to check for sun damage, pests, and other developing problems.
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Formula: Oncidium orchids benefit from a balanced fertilizer, or 10-10-10. The formula of fertilizer required will change depending on the amount of dissolved minerals in your local tap water. Water with total high dissolved solids (TDS) will require fertilizer without these additional minerals, or it may burn the roots. Water with low dissolved magnesium and calcium will require a formula that supplements these essential minerals. The Chicago municipal water supply is very good for growing orchids.
Schedule: Most orchid growers follow a “weakly-weekly” fertilization schedule, and will use ¼ of the package recommended strength, every time they water. Some growers will decrease or discontinue fertilization from late fall to early spring, or when the plant is not actively growing, while other growers may feed evenly year-round. Some growers report success switching to a “bloom booster” formulation in the months leading up to that orchid’s blooming season. The fine roots are susceptible to burn from crystalizing minerals in the water. Flush the pot with plain water without fertilizer once every month to avoid the buildup of fertilizer salts.
Many oncidiums have thin leaves and can develop dark spots on the leaves from an accumulation of excess nitrogen in the leaf tissue. This can be prevented by flushing the pot with pure water one hour later after every time you fertilize.
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Oncidium orchids do not require a dry dormancy or rest period, although their water needs will change with the amount of light provided as seasons change. Some oncidiums may require less water immediately after they finish blooming.
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Use a free draining potting medium like fir bark or a fir bark mix. Adding 20% sphagnum moss to the mix will help it retain enough moisture to last until the next watering, if you don’t want to adjust watering frequency. Some growers have success using lightweight expanded clay aggregate (LECA) or Hydroton in a container that keeps a small reservoir of water, in a method called semi- hydroponic.
Care requirements created with information from the American Orchid Society, and Illinois Orchid Society growers.
