It
is time to prepare for frosty nights and “Orchid Injuring”
cold. While some Orchid species can survive light
frosts, others suffer sub lethal stress at 50 deg. F. It is important to know which to protect and
which plants to leave out awhile. Remember
too, that the forecasts are not always correct so always err on the
side of caution when you decide whether to bring a plant in or light
the heaters in the greenhouse.
Cymbidiums
are one of the most cold tolerant groups even though some come from
warmer areas. Hybrids are almost
certain to be cool tolerant. Many
growers leave their mature Cymbidiums outside in a south-facing location
where they are protected by the overhang of a house or tree until there
are hard frosts. Plants with frost damaged leaves often have
magnificent inflorescences and larger than normal flowers. The same effect can be obtained with temperatures
above freezing. The general recommendation
is to bring plants in if the temperature is predicted to be below 35
or plants are in an unprotected location subject to frost.
Cattleyas,
too, do not mind a nice cool down, but not to the same degree as Cymbidiums. Night temperatures in the lower 50s do no harm
as long as the roots are not wet and the day temperature rises. The key is never let a Cattleya stay damp and
cold 24 hours. If kept dry, most
hybrids do fine even if it gets below 50.
Some species and their hybrids, notable Laelia purpurata and
L anceps, will grow alongside Cymbidiums this time of year and flower
with better colors if allowed to cool into the 40s.
Paph rothschildiana and its
hybrids have the reputation of being difficult to flower. Many books suggest that they must be very large
before they will flower. However,
they will flower readily if they are given a month or two of 50-degree
nights, less water, and less fertilizer.
Once they slow growth and begin to develop an inflorescence raise
temperatures and water as you would other Paphs.
Zygopetalums that develop
new growths when nights are in the 50s generally produce a bloom spike
at the same time. Some species
and many hybrids will flower repeatedly as long as the nights are cool.
Do not limit water and fertilizer for this group
because they seem to stay in a growth mode.
Vandas, Ascocendas, and their
close kin are known to be warm loving, but can take a bit of cold, into
the 50s, if they are dry and are able to warm up the next day. It is not recommended that they be left outside
in conditions continuously below 60 F.
Buds will blast and the plant will go into dormancy if they are
not kept warm during the day or if they get continued cold nights. Some books used to suggest that they would not
flower well if night temperatures were in the 60s. Not only is this not true, but flowers are brighter,
clearer and larger if nights are cool, as opposed to the warm sultry
nights found in Florida. Vanda
coerulea and a few other high elevation species actually like these
cooler nights; a fact that may explain why so many vandaceous hybrids
flower better when nights are cool.
It is important to provide bright light, warm days, and good
humidity if you want your Vandas to thrive during the winter, but they
are not harmed by a few cold nights.
Phalaenopsis are probably
the warmest loving of Orchids, but still need a cool down to initiate
spiking. This is true for most of the large-flowered
species and hybrids, but not for the fragrant summer blooming species
such as Phal violacea and amboinensis.
October is the ideal month to initiate this process and is accomplished
by letting your Phals cool down into the upper 50s or lower 60s. The trick is that they must also warm up the
next day 25 degrees F or more. The
change in temperature is the most critical component in the initiation
of spikes in this group. Most
greenhouse growers find that spike initiation occurs without trying,
but indoors growers may have to consciously create these conditions
to obtain flowers.