Thelymitra ixioides

Spotted Sun Orchid

Logan and District Orchid Society  -  Oncidium Orchids


Oncidium, (abbreviation Onc.) is a genus that contains about 330 species of orchids from the subtribe Oncidiinae of the orchid family (Orchidaceae). As presently conceived (May 2014), it is distributed across much of South America, Central America, Mexico and the West Indies, with one species (Onc. ensatum) extending into Florida.

In 2008, Oxfords Annals of Botany labelled the Oncidium alliance "grossly polyphyletic." The American Orchid Society labelled this genus a "dumping ground." After DNA testing and much debate, a consensus was announced (April 2013) resulting in major taxonomic changes to Oncidium, Gomesa, Odontoglossum, Miltonia, and others. Much of this debate and subsequent housekeeping was initiated by significant research for the scientific publication Genera Orchidacearum Volume 5. One significant change is the move of most Brazilian Oncidium with a fused lateral sepal to the genus Gomesa.  The Royal Horticultural Society system, the World Checklist of Monocots database  and the American Orchid Society have already updated their databases  to reflect most of these changes. (Also Orchid Whiz, which uses these databases as the reference source.) (AOS database is a “Members Only” content. on their website. You must be logged to access this resource)


This genus was first described by Olof Swartz in 1800 with the orchid Oncidium altissimum, which has become the type species. Its name is derived from the Greek word "onkos", meaning "swelling". This refers to the callus at the lower lip.

Most species in the Oncidium genus are epiphytes, although some are lithophytic or terrestrials. They are widespread from northern Mexico, the Caribbean, and some parts of South Florida to South America. They usually occur in seasonally dry areas.

They can be divided in three categories, according to their growth pattern:

Oncidium species are characterised by the following properties :

The flowers of the Oncidium genus come in shades of yellow, red, white and pink. The petals are often ruffled on the edges, as is the lip. The lip is enormous, partially blocking the small petals and sepals.

Some Oncidium orchids are very long : Oncidium altissimum and Oncidium baueri can grow to a height of 5 m, while Oncidium sarcodes can reach 3 m.

They are also known as ' spray orchids' among some florists. They are very varied and are easily hybridised with Odontoglossum. Together with other closely related genera (Cochlioda, Miltonia, Cuitlauzina, Miltoniopsis, Osmoglossum, Leochilus, Comparettia, Cyrtochilum, Odontoglossum, Tolumnia, Rhynchostele [formerly Lemboglossum], Psychopsis, etc.) they form the Oncidium alliance. Some of the best Oncidium alliance hybrids originate from Oncidium tigrinum and Oncidium incurvum, when crossed with Odontoglossums, although hybridizations possibilities of this group of orchids are endless, and there are literally hundreds of thousands of excellent hybrids in the Oncidium alliance.

Growing Oncidiums


Oncidiums are much more forgiving of bright, even direct, light than other popular orchids, especially the phalaenopsis. Oncidiums can handle direct morning light and prefer bright to very bright conditions. They tend to enjoy the same light conditions as dendrobiums.


During the growing season, water daily or every other day. Be careful, though, because drainage is an absolute priority, and 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 very prone to rot. If you see a pseudobulb beginning to rot, cut it out with sterilised cutters and reduce the amount of water. In the winter, reduce watering to bi-monthly or less. They can withstand considerable drought because of their large pseudobulbs. Wrinkled pseudobulbs generally indicate lack of water.


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 11oC Even temps of 14oC will cause the plant to slow its growth if they last too long.


Oncidiums are magnificent in bloom. A large, well-grown plant might send out six or seven branched sprays of yellow flowers. The effect is very much like a cloud of buttery butterflies. The most popular species include O. leucochilum, O. longipes, O. sarcodes, O. pulchellum, as well as many hybrids. Although oncidiums are known for their yellow flowers, other varieties are available. The O. Sharry Baby is sometimes called the chocolate orchid for its sprays of brownish flowers with a rich cocoa scent.

Potting and Repotting:

Oncidiums like to be slightly under potted in a very free-draining bark-based potting media. Many of the 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. In general, only repot when necessary.

Grower's Tips:

Like many orchids, once an oncidium has adjusted to its conditions, they're not difficult plants to grow. Watch your water to avoid rot, make sure the big plants are fed well, give it lots of light, and your oncidium will produce.

ONCIDIUM orchid culture sheets

American Orchid Society Culture Sheet

How I Grow Oncidiums

by Brian Milligan (OSCOV)

Tolumnia Culture

AOS Culture sheet

Oncidium Orchids

Culture sheet by Bribie Island Orchid Society

Enigmatic Oncidiums

AOS Culture sheet


Page updated 17/09/2014.

Oncidium flexuosum Sims


Oncidium Mord Cross

Photo credit:

Onc. Maculatum

Photographed at 62nd Miami International Orchid Show 3/4/2007

Mtssa. Charles M. Fitch 'Izumi'.

Photo credit: Kathy K Jones