Oncidiums are popular indoor and florist orchids for a very good
reason: their large sprays of flowers often sag with dozens of blooms.
There are actually several hundred recognized oncidium species, but the
naming isn't stable, so there is considerable flux as experts reclassify
plants. Additionally, they have been freely hybridized. The most common
oncidium grow well under normal indoor conditions. They have large
pseudobulbs that arise from a mass of thin white roots. The large leaves
(up to 2 ft.) emerge from the pseubobulbs. They flower in fall.
Light:
I
find that 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 I give dendrobiums.
Water:
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 pseubobulbs and masses of
roots, they are very prone to rot. If you see a psuedobulb 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 lack of water.
Fertilizer:
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.
Temperature:
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 tempatures below about 50. Even temps in the mid-50s will
cause the plant to slow its growth if they last too long.
Blooming:
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 underpotted 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. My greatest success with these plants has
come almost by accident: I inherited a very large one and didn't really
have room for it, so I stuck it in the corner of my collection and
essentially forgot about it. That fall, I was rewarded with a profusion
of blooms. Since then, I've enthusiastically grown oncidium. Watch your
water to avoid rot, make sure the big plants are fed well, give it lots
of light, and your oncidium will produce.
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