Humidity and Air Movement..... -- Welcome to Orchids, etc.

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Date Posted: 17:56:26 10/26/00 Thu
Author: Anonymous
Subject: Humidity and Air Movement.....
In reply to: Anonymous 's message, "Temperature and Fertilizing" on 17:54:57 10/26/00 Thu

HUMIDITY

- - HUMIDITY - -

Humidity is moisture that is suspended in the air. The
temperature of the air determines how much moisture it can
hold. Warm air holds more moisture than cool air, so as the
temperature rises, the percentage of moisture in the air
decreases. Because of this, more moisture needs to be added
to maintain the desired level of humidity. When the air
temperature cools, the air gives up its moisture in the form
of rain (or snow if the air is cold enough). Here is a bit of
trivia for you: The driest air on the planet can be found not
in the Sahara Desert, but at the South Pole. Humidity can
be measured using a simple instrument called a hygrometer.
You should be able to purchase a hygrometer at any large
garden center.

Orchids lose water through pores (stomata) found on their
leaves. The drier the air, the faster the orchid will loose its
moisture. Keeping the humidity high reduces the speed of
water loss (dehydration). Orchids prefer a location where
there is a range of humidity between 40% and 70%.

You should not try and keep your humidity at the same
percentage all the time. A fluctuation of humidity is desirable
and gives the plants a chance to "dry out." A 40% drop
during the day for short periods can be beneficial to your
orchids.

- - CONTROLLING HUMIDITY - -

Raising humidity

In a greenhouse, you can wet down the walks and floors
to increase the humidity.

In your home, a humidity tray works very well. A
humidity tray is any kind of shallow container that will
hold water. Just add some pebbles and water. Place the
orchid above the tray making sure the pot does not
touch the gravel. You can also increase the water
evaporation from the tray by adding a heating cable
(sold for germination of seeds) under the gravel. For
more information about humidity trays, please read my
Frequently Asked Questions page.

Group your plants together as much as you can, but not
so close that it prevents free air movement around each
plant. The grouped plants will assist each other in
forming their own beneficial micro-climate cause by their
own evaporation.

Humidifiers work very well. There are many types and
many prices. You will have to see what your budget can
afford and then check out the various types available in
your area. Before investing in a humidifier, however, you
should first invest in a hygrometer to see if you really
need one.

If possible, grow your orchids in the kitchen by the
sink, in the bathroom, the wash room, or anywhere hot
water is used. The evaporation of the water adds
moisture to the air.

If the air is extra dry, you can enclose the orchid in a
plastic "tent". The plastic cover acts like a miniature
greenhouse. Don't make your enclosure air tight, and do
not expose your orchid to direct sun light when it is
enclosed in a tent.

Make sure your furnace and air conditioning units are not
blowing hot or cold air directly on your orchids.

Misting does little for raising the humidity. The water in
the air quickly evaporates. If you insist on misting be
sure and do it early in the day so that any moisture on
the plants leaves will be dry by evening.

Lowering Humidity

Excessive humidity is rarely a problem for orchids grown in
the home. High humidity is usually more prominent in a
greenhouse because of the greenhouse's sealed environment.
This is especially true if you live in an area where the climate
is damp or in and area where winters are dull and cloudy most
of the time.

A sign of excessive humidity or damp stagnant air is the
formation of brown water spots on the leaves, small pink or
brown spots on the blooms, and the flower sheaths turning
black (in extreme cases).

To correct the problem, you need to increase the air
movement with fans to dry out the area. Vent the area to
the outside if the humidity outside is lower than inside. Be
careful not to introduce hot or cold drafts on your orchids
while venting. Decrease watering if possible and DON'T mist.
AIR MOVEMENT
AND
AIR QUALITY

- - AIR MOVEMENT - -

Orchids do not like stagnant air. In their natural habitat,
most orchids grow high up in trees where the breezes are
always blowing. Wind cools the leaves when it is hot, and
helps dry excess moisture that may have accumulated on the
plant. Wind also helps distribute warm and cold air so harmful
air pockets don't form.

Because most greenhouses are very air tight, the need for
mechanical ventilation is a must. Many greenhouses have roof
and/or side vents that can be opened to vent hot air out and
let cooler air in. Some of the side vents may also be equipped
with electric fans. When the temperature reaches a preset
level, the fans turn on and exhaust hot air to the outside.
This not only helps cool the greenhouse but also replaces
stagnant air with fresh air. You may also install a simple duct
system consisting of a large plastic tube that has vent holes
cut into it every two or three feet. A small blower at one
end of the tube blows air through the tube and out the vent
holes. This keeps the air moving in the greenhouse. If the
roof of your greenhouse is tall enough, ceiling fans also work
very well.

In your home, the easiest way to create air movement is to
open a window. Be careful of drafts because they can be
harmful. A draft of cold air can cause buds to drop. If a
window can't be opened, use small fans directed away from
your orchids to circulate the air in the room (ceiling fans
work GREAT).

- - AIR QUALITY - -

Your orchids, like people, need plenty of clean fresh air.

In the home, accumulated air pollutants from pilot lights,
smoking, cooking, aerosol sprays, plastic and other synthetic
materials, people, and other sources can all be harmful to
your plants. To reduce the amount of pollution in your home,
open a window to let fresh air in (of course, you don't want
to open your widows if it is extremely smoggy outside because
you may be letting more pollutants into your home than you
are trying to remove). Electrostatic air cleaners will remove
dust, dirt, and some other pollutants from the air, but are
useless in removing unwanted gases.

You should never smoke around your orchids (they might pick
up the nasty habit the next thing you know, they will demand
to be watered with Jim Beam and start hanging out with
questionable Dandelions--ok, just kidding). If you do smoke,
be sure you wash your hands before handling your orchids to
prevent spreading a deadly virus called Tobacco Mosaic Virus
from your nasty cigarettes to your beautiful orchids.

Ethylene gas can cause the orchid's sepal to wilt--especially
in the Cattleya genus which can be effected by as little as
one part of ethylene gas to 300,000,000 parts of air.
Ethylene gas is produced from incomplete combustion of
petroleum products (coal, natural gas, gasoline, oil etc.) as
well as being produced naturally by some fruits such as
apples. A basket of apples can generate enough ethylene gas
to cause your flowers to wilt and turn black. In a
greenhouse, smog, if brought inside through ventilation, is
very harmful to the blooms because ethylene gas is also
present in smog. If you live in a very smoggy area you may
want to keep your windows closed on the days of high air
pollution. Non-electric (gas, propane, etc.) heaters used in
greenhouses should be vented to the outside.

NOTE:
If your orchid blooms suddenly wilt, it may not be due to bad
air. If the bloom suddenly fades and the petals fold together
and turn papery, an insect may have pollinated the blooms.
Look to see if there is pollinia on the stigma.

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Replies:

Wow! Thank you! I am printing all of this out -- Anonymous, 22:22:48 10/26/00 Thu