[Plant-education] Duckweed Growth Experiment

Janice M. Glime jmglime at mtu.edu
Tue Jun 28 12:58:48 EST 2005

Dear Danny,
  I don't have time to look for references right now, but you can probably
find something with a Google search on the net, using the scientific name.
  Several things could contribute to your problems.  First, you may be
giving the plants an osmotic shock if you move them directly from their
original water to water with added nutrients.  Also, chlorine in tap water
may kill them.  And, it is a plant that grows in lots of light (usually
full sun), so if you are growing it indoors you may need to add light.  On
the other hand, if it has been in the dark or low light for a while, you
need to add light gradually over about a week because it won't have enough
pigments to protect it from high light.
  As you grow it, it will use up nutrients and water will evaporate.  The
best way to care for it is to replace its solution each week to account
for evaporation and nutrient loss.  If it is losing water rapidly, you can
add distilled water to it daily, but you need to replace the original
strength at least once each week.
  What are you using for containers?  It is best if they are cleaned with
an acid, then rinsed well (tap water is usually okay), but they must be
washed with distilled water or your solution water before you put in your
solution water and before the rinse water dries to get rid of chlorine and
other chemicals from the rinse water.
  If you are adding high concentrations of nutrients, you need to add them
gradually.  I would suggest developing a step-up plan where you increase
the concentration a little each day so the cells can adjust osmotically.
At the very least, give them a few hours to adjust before increasing each
time.  If you don't know what their original water concentrations are, you
might try half that water, with half distilled water and add to that for
their basal water.  If you don't have access to distilled water, you can
let tap water sit for 24 hours before using it so the chlorine will leave.
Well water is good, or rain water, but then you won't know what
concentrations you have.  If you are moving fish to a new aquarium, you
need to do the same thing with them - add a little aquarium water to
theirs, then more in an hour or more, then more, until you have mostly
aquarium water in their bag.  Once they adjust to that, and their new
temperature, you can release them in your aquarium.  Otherwise, their
cells might burst because the chemistry is different.  It is like getting
salt in your eyes.  Plants have the same problems.
  If you have not done so, you need to get on the web or go to the library
and find out reasonable concentrations found in ponds with and without
runnoff.  You may be putting an unrealistic concentration in the water.
  Duckweed usually does well in experiments, and it will take over the
surface of a 55 gallon aquarium in a few weeks, so I suspect it is either
getting osmotic shock or chlorine or both.
  Best of luck to you.  Let us know how it works out.

 Janice M. Glime, Professor
 Department of Biological Sciences
 Michigan Technological University
 Houghton, MI 49931-1295
 jmglime at mtu.edu
 FAX 906-487-3167

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