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Oncidium Alliance - warm-growing genera

This varied group of orchids includes plants from many types of 
environments. Some come from hot and dry areas while others 
grow in less severe conditions. More specific instructions may be 
available from the grower. Some genera included are Aspasia, 
Brassia, warm-growing Oncidiums and miltonias 
(often called the Brazilian Type) and many of their hybrids.

LIGHT can be from just bright to almost full direct sun depending 
on the plant. Most will thrive with one to several hours of sun a day.
Generally, thicker-leaved plants can stand more light, such as 
"mule-ear" and "equitant" oncidiums. In the home, east, south or 
west windows are ideal. Many types will grow under artificial light: 
four fluorescent tubes 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 plant. 
In a greenhouse, 20% to 60% shade is required or about 2,000 to 
6,000 footcandles, depending on the plants grown.

TEMPERATURES for this group are generally called intermediate to 
warm: 55 to 60F at night, and 80 to 85F during the day. 
Temperatures to 95 to 100F are tolerated if humidity and air movement 
are increased as the temperature increases.

WATER requirements vary with the type of plant. Generally, plants with 
large fleshy roots and/or leaves need less frequent watering than 
thin-leaved and/or thin-rooted plants. Watering should be thorough, 
and plants should dry at least halfway through the pot before watering 
again. this may be every 2 to 10 days depending on weather, pot size 
and material, type of orchid and type of medium. Plants not actively 
growing should be watered less; many species have winter rest periods.

HUMIDITY should be between 30% and 60%. Most of these orchids require 
less humidity than some other orchids.  In the home, placing the plants 
on trays above moist pebbles is ideal.  Misting the plants in the morning 
may help increase the humidity but is usually not recommended for fleshy 
leaved types.  Most greenhouses have adequate humidity.

FERTILIZER should be applied regularly while the plants are actively 
growing. Applications of 30-10-10 formulations twice a month are ideal 
for plants in a bark-based medium.  A 20-20-20 formulation should be 
used on other media or on slabs.  If skies are cloudy, applications once 
a month are sufficient.  Some growers use a high phosphorous, 10-30-20 
formulation bloom booster as plants approach blooming.

REPOT when new growth begins from the base of the plant, which is 
usually in the spring. A fine grade potting medium is usually used with 
fine rooted plants and coarser mixes with larg-rooted plants; the standard 
size is medium grade. Usually the lowest one quarter to one third of the 
pot is filled with drainage material, either crock shards, rocks or styrofoam 
'peanuts'. The plant is positioned so that the newest growth(s) are farthest 
form the edge of the pot, allowing the maximum number of new growths 
before crowding the pot. Spread the roots over a cone of the potting 
medium and fill in around the roots.  Firm the medium well around the 
roots by applying pressure.  Keep humidity high and the potting medium 
dry until new roots form. 
A vitamin B1 compound may help establish newly potted plants.

"Equitant" and "mule-ear" oncidiums, as well as other fleshy-leaved 
or large rooted plants, can be grown on slabs of cork bark or treefern 
or in pots of a coarse, well-drained medium such as charcoal.

Prepared by the Education Committee, American Orchid Society 
6000 S. Olive Ave., West Palm Beach, FL 33405

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