Oncidium (on-sid-ee-um)

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This varied group of orchids commonly known as dancing ladies is widely distributed throughout the tropical Americas. They grow from sea level to high in the Andes and produce colorful flowers born singly or on stems of 100 blossoms or more. These flowers can last anywhere from 2 weeks to 3 months and when expired should be removed from the plant by cutting the stem off at the point where it emerged from the plant. The following care instructions cover the many related inter-generic varieties and relatives of the Oncidium.

LIGHT
To ensure good growth and profuse flowering, Oncidium requires bright light. They prefer some direct sun and do best when receiving the light source from above rather than from the side of the plant. While growing in your home, a very bright east exposure that receives ample direct sun is ideal, or a south or west exposure where the plant is receiving a few hours of direct sunlight daily.

Oncidium does best when grown outdoors during the months of June through October. Hang them from a tree or the overhang of your house, or place in a screened porch where they can receive some dappled sunlight. Oncidium can benefit from higher intensities of light as the day length decreases towards fall and into winter, and vice-versa for the spring and summer. Try to provide as much light as possible for your plant throughout the year without causing sun burn on the leaves. Once your Oncidium is in the flowering stage it is best to shade it from any direct sun to prolong the life of the blooms.

TEMPERATURE
One important cultural element for Oncidium is that they do best when exposed to a 10 to 15 degree differential between day and night temperatures. It is for that reason we recommend to grow Oncidium outdoors from June until early October. While growing outdoors these plants do not mind periodic temperature dips into the 40’s at night, as long as the temperature rises at least 10 degrees or more during the day. It would be time to bring your Oncidium indoors once the temperature differential between day and night becomes narrow; for example when the October day time temperature is consistently 45 degrees and the nights are 40 degrees. Do not ever allow your Oncidium to freeze.

Once you have brought your Oncidium indoors for the growing season of October through May, it is best to place them in a sunny area that experiences a nighttime temperature of 55 to 60 degrees. In the home this can be best achieved by using a basement area or a spare room that you are able to reduce the nighttime heat source. For the day time, it is still important that the plant experiences a rise in temperature of at least 10 degrees or more. On cloudy winter days an artificial heat source may be needed to achieve the proper daytime temperature differential, while the sunny days should generate enough warmth for an adequate temperature differential.

WATER
Proper indoor watering requires allowing the bark mix to become dry just beneath the surface between watering cycles. Factors such as how root bound your pot is, how much light the plant is receiving, and what size pot it is in, will all play a role on how fast it dries out. Typically while growing indoors a good thorough watering once a week should be sufficient. In cases of root bound plants grown in warm, high light areas, watering every 5 days is needed. When watering, water the bark thoroughly until water runs freely from the bottom of the pot. Always remove your pot from any decorative container to allow for proper drainage. Never allow your pot to stand in any water as this will cause root rot. Never use softened water on any of your orchids.

For outdoor growing it is best to maintain slightly more moisture than for indoors. During the highest temperature periods (mid summer) we recommend to keep the Oncidium moist but not soggy. A watering twice a week is usually needed during that period. As the temperature begins to drop towards the end of the outdoor season, begin letting the bark become dry beneath the surface, much like the indoor watering schedule. While outdoors the natural rain on the plant is beneficial.

FERTILIZER
Oncidium and their inter-generic relatives are fairly active growing plants, and therefore fertilizer is essential for good growth and flowering. We recommend applying a 20-20-20 or similar balanced type fertilizer once every 2 to 3 weeks throughout the entire year. A safe dilution ratio is one level teaspoon of fertilizer mixed in one gallon of water. Do not over-fertilize as this will cause permanent root damage.

HUMIDITY
Like most orchids, the Oncidium enjoys a moderately humid climate of 50% or greater. While growing outdoors this is not an issue since we generally have adequate humidity in our Wisconsin summer climate. While growing indoors it is recommended to increase humidity around the plant simply by placing your plants on a humidity tray, misting them adequately in the morning, or grouping your plants all together in one area.

REPOTTING
We recommend repotting Oncidium once a year, preferably right after flowers expire or right after the start of new growth. If you are not experienced or comfortable doing this yourself we offer the repotting service at our greenhouse for a small fee. Your recently purchased Oncidium may be ready for a repotting job as soon as it has finished flowering. Inquire with us as to when your individual plant was last repotted. Oncidium have a tendency to grow themselves vertically as well as horizontally out of the pot. Good indicators for a repot candidate are: when the rhizome and roots of the plant have protruded over the edge or well above the pot; when the potting medium starts to break down and drain poorly; or when the plant is completely root bound in the pot.

Oncidium may be divided if the plant has enough pseudobulbs to safely do so. A division should consist of a minimum of four pseudobulbs to allow enough strength for future growth. Larger divisions of 6-10 pseudobulbs are acceptable, which in turn will make for a specimen plant the next blooming season. If your plant is not dividable at this time simply repot it into a slightly larger pot.

To make a proper division, start by locating the pseudobulb that had most recently produced flowers. From there, follow the rhizome which connects each pseudobulb and count back from there four to five pseudobulbs. At that point, cut the rhizome and root mass using a pruning sheer or large stiff knife to make your division. Repeat this process with the remaining portion of the plant. After doing that, you may have a clump of leftover pseudobulbs called back-bulbs. These will not have a recently flowered pseudobulb attached and are not viable or worthy of potting and should be discarded.

A note about orchid viruses: most commonly the transmission of orchid viruses is caused by using the same cutting tool on multiple plants. The most effective method to reduce virus transmission from plant to plant is to briefly flame sterilize all your cutting tools between use on each plant. A simple Butane torch or a gas stove are handy items for this purpose. This practice should be implemented when repotting as well as when cutting off expired flowering stems.

Once your division is made, select a new pot in the appropriate size to allow for another year of growing. Unfortunately, there is not a set rule for choosing the proper pot size, but generally you will need to increase the pot size by one to one and one half inches. Do not use too large of a pot because these plants like to be somewhat crowded, even after repotting. Place the cut side of the division against the inside perimeter of the pot and fill the pot with our moistened fir bark orchid potting mix. Try to keep the rhizome about 1/2” below the potting mix and pack it firmly with a blunt tool to ensure the plant is secure in the pot. Wait about one week and then water thoroughly.

For more assistance with your Oncidium or any other Orchid, please call us at 608-831-4700, send an email, or visit our store.

Happy growing, from Orchids Garden Centre & Nursery!