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Oncidium
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.
Light 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
footcandles, 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.
Temperatures
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 rule is any case.
Water
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.
Humidity 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.
Fertilize
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 formulations should be
used on plants in other media or
on slabs. If skies are cloudy,
applications once a month are
sufficient.
Potting 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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