Effect of Humidity on plant growth

Ross Koning Koning at ECSUC.CTSTATEU.EDU
Wed Nov 27 14:47:05 EST 1996

At  5:33 PM 11/26/96 -0500, Ben Linderman wrote:
>I am a 10th grade student that needs help for a science project.  I need help
>finding information on the effect of humidity on plant growth.  My teacher
>gave me no help saying I had to do it on my own.  Please help me.


Why not do an experiment to answer the question
for yourself?  It is the best way to learn...and
more fun too!

You will need some pots, soil, a semi-sunny window
(or maybe better, a fluorescent shop light), some
plastic wrap, tape, wire coat hangers, and some seeds
(I would recommend some dry red kidney beans from
the grocery store).  Use the wire to make cages
that fit in or around the pots.  All the pots need
a cage.  Some (not all?) will need plastic applied
to enclose the plants.  You might leave the top open
on one and completely enclose two others.  If you have
a hand sprayer you can periodically mist (at least a
few times a day) inside one enclosure with water.

The soil should be the same for all the pots, you
might use a tray and water from the bottom, so all
the pots have good accessibility to water for roots.
Be sure the soil isn't soggy, though, or plants die!

The sunny window would probably be more trouble as
you have thermal problems and greenhouse effects...
the fluorescent light is cooler and less likely to
cause greenhouse effects.  It needs to be within a
half-meter of the plant leaves!  To avoid criticism
you should probably monitor temperature in each cage
(add a thermometer to the list).  If your teacher
can provide you two thermometers, you can make
one thermometer a wet-bulb thermometer by wrapping
the bulb of it with wet cheesecloth or cotton batting.
You probably need to calibrate the thermometers (do
they read the same when both are dry? If not, be sure
to add or subtract from the reading of one thermometer
as needed).  The wet bulb thermometer responds very
slowly to change, so you have to leave it in each
cage for a long time before taking a measurement.
If your school has the luxury of several thermometers,
great!, keep separate wet-bulb ones in each enclosure.
There are tables (handbook of chemistry and physics)
that can help you convert the difference between a
wet-bulb and dry-bulb temperature reading into a
humidity measurement.

You will want to use more than one plant in each
condition, and take several different kinds of
measurements.  Height is good, but sometimes misleading;
plants in trouble often grow incredibly long and
spindly.  Leaf width (at widest point) might be
a good coordinating measurement.  Of course bean
plants have more than one kind of leaf, so you
have to measure and compare leaves correctly
(simple primary to simple primary for example).

Terminal fresh weight and dry weight measurements
could also be useful.  Dry weight requires you to
bake the plant tissue in an oven (250 F) for at
least an hour to dry the tissue.  Obviously you
can only do that at the end of your project.  Of
course fresh weight is also an end-of-project
measure also, since you want to weigh plant-only!

Maybe your teacher has some other ideas.  If s/he
finds out you want to answer your question with
a real project, s/he will probably be thrilled to
help you with it.

Good Luck!


Ross Koning                 | Koning at ecsu.ctstateu.edu
Biology Department          | http://koning.ecsu.ctstateu.edu/
Eastern CT State University | Phone: 860-465-5327
Willimantic, CT  06226  USA | Fax: 860-465-5213

                Plant Physiology is Phun!

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|  |  |  |    |  |  ||       //\___     \CH3     /\|/\\/\\COOH
 \/ \/|\/|    \\/ \ /       N  ||  N            |  |
 /\ | |__|=        NH       |  || ||           //\//\
  | COOH                    \\ /\ /            O
  COOH        H2C=CH2         N  NH

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