This is an extraordinarily
large and diverse New World genus with an equally
diverse number of habitats. Oncidiums may
originate anywhere from sea level in the tropics
to the high elevations of the Andes. This
obviously makes cultural generalizations
difficult. More specific instructions may be
available from the grower. Some genera included
are Aspasia, Brassia, warm-growing
miltonias (often called the Brazilian type) and
many of their hybrids.
L I G H T
needs can vary from bright to nearly full direct
sun depending on the species. Most will thrive
with one to several hours of sun a day.
Generally, thicker-leaved plants, such as
"mule-ear" and "equitant"
oncidiums, can stand more light. In a greenhouse,
20 to 60 percent shade is required, or about
2,000 to 6,000 foot-candles, depending on the
plants. In the home, east, south or west windows
are ideal. Many types of oncidiums will grow
under artificial light: Four fluorescent tubes
supplemented with incandescent bulbs and placed 6
to 12 inches over the plants are necessary for
proper growth. Metal-halide and sodium-vapor
bulbs also provide sufficient light without
needing to be so close to the plants.
for this group are generally considered
intermediate to warm: 55 to 60 F at night, and 80
to 85 F during the day. Temperatures up to 95 to
100 F are tolerated if humidity and air movement
are increased as the temperatures rise, a good
general role in any case.
W A T E R
requirements vary with the type of plant.
Generally, plants with large fleshy roots or
leaves need less-frequent watering than
thin-leaved or thin-rooted plants. Watering
should be thorough, and the medium should dry at
least halfway through the pot before watering
again. This may be every two to 10 days depending
on weather, pot size and material, type of orchid
and type of potting medium. Plants not actively
growing should be watered less; many species have
winter rest periods.
H U M I D I T Y
should be between 30 and 60 percent. Many
oncidiums require less humidity than other
orchids. Most greenhouses have adequate humidity.
In the home, placing the plants above moist
pebbles in trays is ideal.
F E R T I L I Z E
regularly while plants are actively growing.
Applications of 30-10-10 formulations twice a
month are ideal for plants in a bark-based
potting medium. A 20-20-20 formulation should be
used on plants in other media or on slabs. If
skies are cloudy, applications once a month are
P O T T I N G
should be done when new growth is about one-half
mature, which is usually in the spring.
Fine-grade potting media are usually used with
fine-rooted plants and coarser mixes with
large-rooted plants; the standard size is medium
grade. The plant should be positioned in the pot
so that the newest growth is farthest away from
the edge of the pot, allowing the maximum number
of new growths before crowding the pot. Spread
the roots over a cone of potting medium and fill
in around the roots. Firm the medium around the
roots. Keep humidity high and the potting medium
dry until new roots form. Equitant and mule-ear
oncidiums, as well as other fleshy-leaved or
large-rooted plants, can be grown on slabs of
cork bark or tree fern or in pots filled with a
coarse, well-drained medium such as charcoal.
This allows the drying between waterings that
these types need.
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