Winter in the temperate zone is alien to most tropical
Orchids.
For the most part, tropical
Orchids experience nearly 12-hour days and nights with only slight differences
in day length and or temperature.
With the exception of species at the end of the tropical zones
or those from high elevations, the most likely seasonal variation many
species will experience is that of a wet/dry variation during the year.
Remember, for tropical species, dry may simply
mean less wet, while in other cases there may be little or no moisture
for months in their natural habitat.
Failure to recognize this aspect in both species and hybrids leads
to either poor growth or death in many Orchids.
If you have graduated to species
or have primary hybrids (those made by combining two species), you may
find that a little research can lead to much improved growth and flowering
in these plants. If you find
that the natural habitat offers clear days during winter, take this
as a hint that the species requires bright light and less water during
that time of the year. Some species are more forgiving than others
and so are more common in cultivation, while hybrids have been selected
that withstand conditions in greenhouses.
There are some common groups of Orchids that respond to simulated,
pronounced seasonal change and that give many growers, novice and experienced
alike, difficulty.
In Paphs, the diminutive Brachypetalum
group (concolor, niveum, etc) grows in limestone outcrops subject to
dry periods and rapid drying. In
winter, when day length is short and light intensity low, members of
the Brachy group must be watered less.
This group has thickened leaves that store water.
If the root system is intact, let the leaves shrink a little
before watering. The same is true of most of the Parvisepalum
group; water them less in winter and watch the leaves for a sign that
they need water.
Many Cattleyas, including
hybrids need to be drier in winter.
Increasing light intensity in greenhouses will assist in drying
the plant and simulates aspects of their natural environment.
Encyclias and other Caribbean species are in the hurricane zone
with heavy summer rain ending in late November or early December. For the next six months there is little rain,
but high humidity. Sunlight
remains relatively intense and days near 12 hours long. Failure to limit water leads to the loss of
many Caribbean Orchids in temperate greenhouses each winter.
Under-lights growers have
an advantage this time of year as they can more effectively control
both day length and light intensity.
If you grow hybrid Orchids inside, do not try to replicate the
day length here in the Carolinas. Eleven
hours of light is a short enough day to convince your plants that they
are at home. Depending on the heating system in your home
there may even be a need to add humidity to your growing area. Orchids prefer the kind of humidity that people
like, about 60%.
Some Orchids grow in habitats
that experience little seasonal change.
Vandas and Phals will grow great under the same conditions year-round,
65 F at night and 90 F during the day.
Both of these groups like long days with Phals preferring lower
light levels. Remember that
standard Phals need large day/night temperature change, and/or lower
night temperatures to initiate flowering.
After that period of flower spike initiation, these Orchid groups
need conditions similar to the warm tropics.
One final warning before winter
officially arrives. If you have
discovered a few more critters missed before moving plants inside or
into the greenhouse, there is still time to spot-treat them on a nice
warm afternoon. Some pesticides are not approved for inside
the greenhouse and some that simply stink.
Move affected plants outside in an area away from pets, children
and bright light and treat following directions.
The low humidity will help the plant dry and loose at least some
of the smell that often accompanies these pesticides.
After plants have passed the “no contact period” (see
pesticide directions) move them back inside or in the greenhouse and
place them where you can watch them during the winter in case some of
the beasts survive.