Light A good indication of
proper light is the color of the leaves: they
should be bright green as opposed to dark green
(too much shade) or reddish green (too much
light). I have often moved a plant that was large
and strong, but which had not yet bloomed, into
brighter light conditions and watched as it
responded almost immediately by sending up
spikes. Care must be taken when doing this,
however, that the increased light is not too
great or injury to the leaves will result.
Temperature If your
temperatures are seldom above 100 F or below 45
F, then temperature-tolerant Oncidiinae should
Humidity Provide a humidity
range of 50 to 90 percent. Seedlings benefit from
70 percent or higher humidity. Generally,
humidity should be increased as temperature,
light intensity and air movement increase. This
can be accomplished by misting the plants and
periodically wetting down the greenhouse floor
Air Movement Adequate air
movement reduces leaf temperature, thereby
allowing high light intensity and more vigorous
growth. An additional advantage is the reduction
of fungal and bacterial infections, which high
humidity alone might otherwise cause.
Oncidiinae intergeneric hybrids should be kept
somewhat moist. Never allow them to dry out
completely, but be sure to provide for excellent
drainage, as soggy or waterlogged conditions are
not conducive to healthy growth. Generally, they
require more water when making new growths, and
less once the pseudobulbs have developed. When
watering, be sure to water copiously to ensure a
thorough wetting of the potting medium, and to
reduce the buildup of toxic minerals.
Fertilizing These plants
respond favorably to a balanced formula, such as
20-20-20, at 1/2 strength, every second or third
watering. If potted in fir bark, a high-nitrogen
fertilizer, such as 30-10-10, will be required.
Fertilizing can generally be increased during
warmer weather when plants are in active growth,
while the reverse is true in cooler months.
Potting As a rule, repot every two years.
Exceptions are those plants in rock wool or
mounted on tree-fern slabs or cork bark; these
should be repotted only when the medium starts to
break down or the plant has outgrown the slab.
Plants potted in sphagnum moss may need to be
repotted every 12 to 18 months. While both
plastic and clay pots offer advantages, the
heavier clay pots are suggested for plants with
tall spikes to help prevent plants in flower from
tipping over. Repot when new growth is 2 or 3
inches tall or when the new roots first appear.
Remove any organic mix and trim off dead roots
with a sterilized blade. If it is necessary to
divide, keep at least three to five mature
pseudobulbs together. Water the newly repotted
plants lightly until the new roots have
penetrated the medium, then resume normal
watering. Pot size will depend on the size of the
plant and its root system. Small, shallow pots
allow room for one- or two-years growth.
Potting Media Any porous mix
with good water-retentive qualities can be used.
Our preferred medium is rock wool, an inert
material made from molten spun rock. We combine
two parts Grodan Stone Wool with one part
expanded perlite with excellent results. The
advantage to rock wool is that it will not break
down, and thus can be left on the root system
indefinitely if particular attention is paid to
flushing the medium routinely with pure water to
remove accumulated salts. Other possible media
are New Zealand sphagnum moss, tree fern, fir
bark, and all sorts of combination mixes. The key
is not to allow them to completely dry between
waterings. Keep them slightly moist at all times
while providing good drainage. Primary hybrids
with Brazilian miltonias do well in
fingernail-size horticultural charcoal.
Milton O. Carpenter.