The Plant Man column
for publication week of 11/30/03 - 12/06/03
(726 words)
###

The Plant Man
by Steve Jones
www.landsteward.org

"What exactly is solarizing?" That was a question that was sent to me
recently by a reader of this column. Because the subject is somewhat
unusual and the results are very effective, I thought I would share
the answer with you today.

"Solarizing" might sound like a cosmic phenomenon or something you'd
do to the windows in your greenhouse or conservatory. However, the
real definition is, quite literally, much more "down to earth."

A simple definition of solarizing could be the act of trapping the
heat from the sun and concentrating it on garden soil in an enclosed
environment.

Most often, solarizing is used to kill off weed seeds in the soil
without having to revert to chemicals. Many landscapers and gardeners
also use solarizing to kill off harmful organisms and fungi that are
otherwise quite difficult to get at.

Solarizing is quite an easy project for even the most
"horticulturally-challenged" person! And it's also quite fun. All you
really need are some sheets of clear plastic, preferably from 1 to 4
mil thick.
You'll need to get twice the square footage of the area you intend to
cover.
Most major hardware chains and garden centers sell it in rolls or by
the foot and you can usually find it in various widths. You'll also
need some objects to use as "spacers." More on those in a moment.

Start by tilling the soil, either manually or using a rented rotary
tiller, then roughly rake the surface so it's fairly level. Then give
it a good watering. I mean a REAL soaking, so the water goes down
about 12 inches or so.

Now cover the entire area with half of the plastic sheeting. You're
going to add a second layer of plastic sheeting but you're going to
want to create some air pockets between the two layers which is where
the spacers come in.
You can use bricks, smooth rocks (without any sharp edges that might
tear the sheeting) or empty 12-ounce beverage cans.

Invite a couple of friends over to help you "empty" the beverage cans.
Or if you worked up a particular thirst with all that tilling and
raking, you can drain the beverages from the cans all by yourself.
Tell your spouse that this is an essential step in ridding the soil of
weed seeds and fungi. It's worth a try.

Spread the spacers evenly on the surface of the first sheet of
plastic, maybe around 18" apart. If you're using bricks or cans, lay
them on their sides, not upright. Now place the second sheet of
plastic over the first sheet and your rows of spacers. It doesn't
matter if the two sheets touch each other in places between the
spacers, but you do want to create a fairly sizable air-trap between
the sheets.

Now all you have to do is seal the two sheets of plastic to the
ground.
Scoop soil up and over the perimeter of the sheeting. You can augment
the soil with some bricks or smooth stones if you think the plastic
sheeting is in danger of being blown away by strong wind gusts.

Leave the "solarizer" in place for a month or two (the longer the
better) and when you finally remove it, your soil should be free of
weed seeds, fungi and soil-borne pests such as nomatodes.

Because this process only works by using the sun's heat to raise the
soil temperature enough to kill off all the bad stuff, this generally
is NOT a project for the winter months, depending on your location.
After all, if the plastic sheeting is covered by frost or snow, the
sun's rays can't do their job.

However, the winter is a good time to plan ahead. In December and
January you can decide which areas of your landscape would benefit
from a solarizing treatment in the spring or summer. You can also
start work on emptying those beverage cans you are going to need as
spacers!

Hey, I told you that this was a fun project, didn't I?

The Plant Man is here to help. Send your questions about trees, shrubs
and landscaping to and for resources and
additional information, including archived columns, visit
www.landsteward.org where you can also subscribe to Steve's free
e-mailed newsletter.