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Date: Fri, 12 Dec 1997 10:02:04 -0700
From: Charles & Margaret Baker <cmbaker@teleport.com>
Subject: [17246] Re:[17213][17130] Humidistats and Humidity - mini faq

Hi June,

Paul, you couldn't be more "right on."

Humidistats and Relative Humidity
=================================
A mini FAQ
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As a lifelong weatherman, forecaster, and tender of professional
weather equipment, Charlie says that humidistats are so unreliable
as to be essentially worthless for determining relative humidity.

It is nearly impossible to keep even the most expensive, highest
quality equipment calibrated. The best quality indicators and
humidistats are based on the expansion and contraction of a human
hair, which is relatively dependable for awhile, but over time,
the accuracy decreases. Cheap humidistats usually use horse hair
to provide the expansion and contraction caused by the amount of
moisture in the air. Horse hair gives only marginally accurate
readings, especially after it has been in use for awhile, even
a relatively short time. This is true even if they are good
quality (read expensive :) in the beginning.

With that said, we do use a humidistat, the cheapest one we can
find. The least expensive we've found is $4.25 from Charlie's
Greenhouse Supply in Mt. Vernon, WA. (Usual disclaimers apply,
no benefit to us.) We have several scattered around the green-
house and use them to indicate the level of moisture _relative_
to the reading of the preceding day. Comparing a reading to a
prior reading is the only way we use a humidistat. The
direct-reading, absolute number is worthless.

Comparing humidistat readings from day to day is an easy way to know
when we need to water. If the "reading" drops lower than it has been
during the day and doesn't come up to regular levels at night, we know
that our plants need to be watered. Using it this way allows you to
become accustomed to any gradual changes in the reading, so it doesn't
matter exactly what the number is or if it is accurate, all we care
about is that it dropped below the normal readings during the day and
didn't increase enough when temperature cooled at night.

We don't wait this long for plants in small pots, or for plants that
must stay moist. We do try to match the potting medium with how
quickly the pot disburses water and how moist the roots like to be,
this reduces the need to fuss with the plants too much.

If you want an absolute percentage number, the following might give
you a rough guide. If you walk into the greenhouse in the morning,
after the temperature has dropped overnight, and the humidistat reads
50%, the humidistat is reading too low. Except perhaps in extremely
dry, desert climates, humidity should be at least 75-80% early in
the morning, especially if you watered the day before. If any
condensation occurs, humidity is essentially 100%.

Our climate has relatively warm, dry summers, it works well for us to
use the prevailing temperature in the greenhouse as our guide to when
we need to increase the amount of moisture in the air (humidity). Warm
temperatures and low humidity go hand in hand for us. When it gets
warm, about 80F (27 C), we use an evaporative cooler and mist the
walkways and in front of a fan to provide cooling and also increase
humidity. Charlie hooked the control for the mist system and the
huge fans to come on at almost the same time. Doing it this way means
that we need only one thermostat to cool and maintain humidity in
the growing area.

Don't forget, the greater the humidity, the more critical it is to
have excellent air circulation to help the plants dry after watering
and prevent fungal infections. Our air circulating fans operate 24
hours a day, year round, but we also have large fans to further
increase the volume of circulating air when we mist to cool the
growing are or increase humidity.

Where we live, in the Pacific Northwest which is basically a temperate
rainforest, winter is so wet and humid that we commonly approach
100% humidity outdoors and close to that in the greenhouse. We
avoid watering for as long as possible because we don't want
condensation with the resulting risk of disease. Also, orchids are
very efficient at grabbing moisture out of the air, so water can be
applied less frequently.

It might be worth your effort to try to make a similar correlation's
in your own growing area. Check with your local TV station, they may
even be on the net, ours are. Get a feel for seasonal variations in
humidity, as average humidity increases and decreases with changes
in temperature.

We grow our warm-loving plants indoors. Even with a radiant heating
system and extremely high humidity outdoors, humidity inside is
approximately 30% in winter and 40% in summer. (This assumes an
inside temperature of about 70F (21C).) If you have a forced air
heating system, or live in a very dry climate, humidity is even
lower.

If condensation occurs at night, humidity is close to 100%. This
is true regardless of the temperature. Ideally, humidity should be
below the level where condensation occurs, especially when growing
indoors. Preventing condensation helps prevent plant disease, but
even more importantly, it avoids damaging wood surfaces in your
home. We increase humidity indoors by directing the air from a fan
directly over the surface of a container of water. Pebbles that are
partly above the water in the bottom of a tray increase the surface
area from which moisture can evaporate.

Every growing area has tiny microclimates which can help a plant be
as healthy as possible.

As plants release moisture, they raise the humidity in their
immediate area. You can use this small microclimate to best
advantage by placing any soft-leaved plants in the center of a
plant grouping so that it receives the highest possible humidity.

On the other hand, plants on the outside of a grouping will dry
faster, which is beneficial for many orchids. These are just two of
the many small microclimates that occur in every growing area.

We hope this helps. We will post it on our website. :)

Cheers, Marg and Charlie

>From: Robert Pavlis <rpavlis@labtronics.com>
>Subject: [17213] [17130] humidity

>You asked about checking the accuracy of your humidity meter.
>
>Can't really answer your question, but have a story to tell. I went to
>buy a humidity gage for my plants. The store had two types with several
>of each. through the package you could read the humidity value of each
>one. There was about a 30% difference between the low and the high in
>the bunch. These were not good lab types, but the type you would find at
>your local hardware store. I did not buy one.
>
>Robert Pavlis         President            rpavlis@labtronics.com
>Labtronics Inc.                           http://www.labtronics.com

Orchid Culture & Pollination site   http://www.teleport.com/~cmbaker/
---
Charles & Margaret Baker, Portland, Oregon USA (cmbaker@teleport.com)
        "Orchid Species Culture" books printed by Timber Press
#1 Pescatorea, Phaius, Phalaenopsis, Pholidota, Phragmipedium, Pleione
HardcoverISBN 0-88192-189-0 $32.95 |SoftcoverISBN 0-88192-208-0 Out/print
#2 Dendrobium
HardcoverISBN 0-88192-360-5 $99.95 |SoftcoverISBN 0-88192-366-4 $59.95

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Date: Sun, 14 Dec 1997 01:43:50 -0500
From: Ruth Rudkin <100247.256@compuserve.com>
Subject: [17263] Address for A. Hicks.

Aaron Hicks could not remember the address of the place where tissue
culture was being used to propogate Cypripedium acaule. I met the girl who
was doing this and the address is Katie Sokolski, c/o Peter Faletra,
Lin-Wood School, Lincoln, NH 03251. She gave an excellent report to the
Orchid Conservation conference in Florida last June.

Hope you contact the school.
Ruth, Sydney.

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