Oncidium, genus of some 300 species of tropical and subtropical American orchids (family Orchidaceae). The plants vary greatly in size and shape, and most species are epiphytic. The pseudobulbs typically have several bracts and bear one to three leaves.
During the growing season, water daily or every other day. Be careful, though, because drainage is an absolute priority. The potting media must be perfectly free draining. The plants can also be grown on slabs or in baskets. Because oncidiums have large, fleshy pseudobulbs and masses of roots, they are prone to rot. If you see a pseudobulb beginning to rot, cut it out with sterile snippers and reduce the amount of water. In the winter, reduce watering to bimonthly or less. They can withstand considerable drought because of their large pseudobulbs. Wrinkled pseudobulbs generally indicate a lack of water.
Oncidiums are much more forgiving of bright or direct light than other popular orchids, especially the phalaenopsis. Oncidiums can handle direct morning light and even prefer bright to very bright conditions. They tend to enjoy the same light that dendrobium orchids prefer.
During the growing season, feed with a weak orchid fertilizer bimonthly or scatter slow-release pellets in the growing media at the beginning of the season. Although there are many species, in general, the larger the plant, the more heavily it will feed.
Oncidiums can be found in many habitats, from semiarid subtropical lowlands to cool and misty cloud forests. Generally, the most popular oncidiums, which feature small yellow flowers, large pseudobulbs, and strappy leaves, are intermediate to warm orchids. Do not expose them to cold drafts or temperatures below about 50 F. Even temps in the mid-50s will cause the plant to slow its growth if exposed long.
Oncidiums like to be slightly underpotted in a very free-draining bark-based potting media. Many oncidiums will form large clumps of pseudobulbs and develop into rather large plants. They can be easily divided into clumps when repotting. Just make sure you have at least three pseudobulbs in each division.
