Weed Control in Home Gardens - Cultural Weed Control

Cultural Weed Control
Most cultural methods of weed control emphasize prevention.
These include mulching, solarization, and multiple
or wide-row planting.
Mulches
Any layer of material spread over the soil surface
may be considered to be a mulch. There are two classes of
mulch: organic and inorganic. Both reduce weed growth,
retain soil moisture and influence soil temperature.
Hay, straw, sawdust, ground bark, leaves, compost and
even newspapers are among the many substances utilized
as organic mulches. All reduce weed emergence and make
it easier to pull those weeds that do emerge. Some weeds
such as nutsedge will grow through mulch, even through
plastic mulch. Extension factsheet SP 291-H,
Mulching
Vegetable Gardens, contains additional information regarding
the use of mulches in home gardens.
Inorganic mulches include black and other opaque plastic
as well as landscape fabric. Landscape fabric is much
more expensive than plastic mulch. However, it has the
advantage of allowing water to pass through into the soil.
Black plastic (polyethylene) is the most commonly used
inorganic mulch. Clear or translucent plastic should not
be used as mulch. These plastics allow light to penetrate,
which permits germinated weed seed to grow under the
plastic mulch. Black plastic eliminates growth of most, but
not all, weeds. For example, yellow nutsedge will grow
through plastic mulch. Also, weeds will grow in the holes
cut in the plastic for the vegetables. More information regarding
the proper time and method of application, as well
as the advantages and disadvantages of plastic mulches, just search below.
Opaque plastic in colors other than black is sometimes
used as mulch and will also control weeds. However, many
of these plastics are quite expensive. Some data suggests
that tomatoes grown on red plastic or that muskmelon
grown on blue plastic will produce higher yields. Yield
increases of up to 25 percent have been documented. However,
the results are not consistent enough to justify the
expense of the colored plastics.
Due to high temperatures and intense solar radiation,
the use of black plastic may cause damage to plants transplanted
or seeded during the hottest part of the summer.
White plastic can be utilized during the summer months to
prevent root and stem damage to the plant. White plastic
will allow light to penetrate. Therefore, white plastic with
a black backing (known as white on black) is preferable.
White on black plastic is more expensive and may be diffi
cult for home gardeners to locate in affordable quantities.
Another option is to whitewash or paint the black plastic
with white latex paint. The paint will eventually wear off,
but not until the plants have shaded the plastic around the
base of the plant, reducing the chance of damage.
Solarization
Solarization is the use of clear polyethylene plastic
sheeting (2 to 6 mils thick) to capture the radiant energy of
the sun, thereby raising the soil temperature to levels lethal
to many weed seeds. The plastic sheeting is placed over
bare, moist soil during a summer fallow period. In Tennessee,
best results are obtained by using two layers of plastic
sheeting and separating the layers with boards, bricks or
small squares (ca. 3” X 3”) of polystyrene insulation called
spacers. Spacers are placed every 1.5 to 2 feet on top of the
fi rst layer of plastic. The second layer of plastic sheeting is
then placed on top. This creates an air gap between the two
layers, which provides a reservoir of warm air that minimizes
nighttime cooling. The two layers of plastic sheeting
are then sealed together by placing soil along the outer
edges of the top layer.
The top layer of plastic should be kept clean to maximize
solarization effi ciency. An occasional dusting with a
dust mop or rinsing with a garden hose should be all that
is necessary. The plastic is left in place for 4 – 5 weeks.
During this period, soil temperatures are frequently raised
to 120 – 125 degrees F. This practically eliminates viable
weed seed in the top 2 to 3 inches of soil. After the plastic
is removed, care must be taken not to mix the deeper layers
of unsolarized soil with the nearly weed-free solarized soil.
Rototilling no deeper than 1 – 2 inches is recommended.
As long as the soil is not rototilled deeper than this, weed
control by soil solarization can signifi cantly reduce weed
infestations for 12 months or more. Many soil-borne plant
pathogens will also be reduced during the solarization process.
This improves plant stands and vigor and may double
yields.
The best time to solarize soil in Tennessee is from May
through early August. Two or three periods, each consisting
of several days in a row of warm weather and bright sunshine,
are necessary. Late summer and fall vegetables may
be planted the day after removing the plastic.
Multiple or wide row planting
Closely spaced double or triple rows may also assist in
weed control. Simply plant two or three rows of a vegetable
close enough so that the leaves will cover the area between
them rapidly as the plants grow. Very small vegetables such
as radishes may be broadcast in a long row a foot or so
wide. These techniques allow growing vegetables to shade
the soil, which reduces weed growth.