How to Use Solarization to Prepare Areas for Planting


There are many options for preparing an area
for a pollinator habitat planting. Good site preparation is key to successful
germination and establishment of native wildflowers. In this video, we’re going to talk
about how to use solarization to kill weeds and weed seeds in the topsoil before sowing
wildflower seeds. Solarization uses a clear sheet of plastic
laid over the ground to trap heat from the sun and kill weeds, seeds, and pathogens in
the top few inches of soil. It’s a safe, non-chemical approach to weed
eradication that can be used in both garden and farm settings. When carried out correctly, solarization is
a highly effective weed eradication technique. Before we go through the detailed step-by-step
approach to using solarization, let’s walk through some of the considerations when deciding
whether solarization is the right tool for your planting area. Why might you choose solarization over other
site preparation techniques, such as herbicide applications or repeated tillage? You might use solarization if:
You live in a hot, dry climate. In areas like California’s Central Valley,
solarization is more effective than any other weed control method, including herbicide control. In other climates, it’s effective for sunny,
well-drained sites. Solarization is a great option to consider
if you want an organic method, if you don’t need to control rhizomatous, woody,
or hard-seeded weeds, or if you have a long and narrow or small planting site. Solarization is easier and more cost effective
for sites under a half-acre in size. And if you’re willing to invest resources. Purchasing new UV-stabilized solarization
plastic can be costly. If you have a source for used high tunnel
plastic in good condition, this can be much more affordable. Now that you know some of the considerations for
how and where you might want to use solarization to prepare a site for planting, let’s talk
through the detailed steps of the process. Step 1: Obtain plastic
In general, solarization is best done with clear plastic, rather than black plastic,
in order for solar radiation to penetrate into and be trapped within the top layer of
the soil. The plastic needs to be thick enough to withstand
breakdown by UV rays, wind, and other disturbances through the growing season. We recommend using UV-stabilized greenhouse
polyethylene plastic with a thickness of 4 or 6 mil, which can be ordered from a variety
of agricultural suppliers. Used high tunnel plastic in good condition
can be reused for solarization, reducing the total cost of the project. Make sure to repair any rips or tears with
greenhouse plastic repair tape. In small areas, consider adding a second sheet
of clear plastic to maximize solarization temperatures and efficacy. This option is not likely to be cost effective
for larger plantings. Step 2: Prepare the planting area for plastic
In early spring, mow and rake off existing vegetation, then disk or till the soil to create an even
surface for the plastic. Loosening the soil will also help with burying
the edges of the plastic. If your soil is dry, you’ll want to irrigate before solarizing to encourage germination of weed seeds underneath the plastic. Just before you’re ready to lay down the
plastic, dig a trench at least 4” deep around the border of the planting area. To save time, consider using a walk-behind
trencher (such as a Ditch Witch), which can be rented from any major home and garden store. For larger plantings, trenching can be done
with a variety of tractor implements. Step 3: Lay down the plastic and bury the
edges Once the area is prepared, roll the plastic
out by hand or with rolling equipment attached to a tractor or ATV. Spread the plastic out until it’s taut,
minimizing any air pockets at the soil surface. Place the edges of the plastic in the trench
and cover with soil to bury the edges down to at least 4 inches, or enough to keep the
edges buried for the time that the plastic is on the ground. This prevents airflow underneath the plastic,
which can significantly reduce the radiant heat and weed kill under the plastic. If there are any places where two pieces of
plastic come together, make one trench along the seam and bury both pieces of plastic in
the trench together with several inches of overlap. Make sure to get a good seal along this edge. Step 4: Perform minimal maintenance through
growing season Check plastic for rips and tears through the
summer. If your area has abundant deer populations,
be prepared for animal damage. Promptly repair any rips with greenhouse plastic
repair tape. Mow around the edges of your solarization
site to keep weeds around the future planting area from going to seed. Alternatively, plant an annual warm season cover crop or insectary strip mix around the edges of the plastic. Step 5: Remove the plastic in preparation for seeding.
How long do you leave on the plastic? In most areas, solarization plastic should
be left in place from late spring through mid-fall. In cooler climates, keep an eye out for rhizomatous
weed growth under the plastic in fall and be careful not to leave the plastic down too
long. In early fall, assess any weeds remaining
under the plastic. If there are any aggressive perennial weeds
still growing underneath the plastic, you may need to leave the plastic on and solarize
for a second season. If not, you’re good to go. Before removing the plastic, pull or mow any
weeds around the edges of the plastic that might rain seed into the solarized area. Roll back the plastic and set it aside for
reuse or recycling. Hand pull any remaining perennial weeds or
annual weeds that might drop seed into the planting area, taking care to minimize disturbance
to the soil surface. Do not cultivate the soil prior to seeding,
or you risk bringing up new weed seeds from below the soil surface. Take care not to spread the untreated soil
used to bury the edges onto the solarized area. Step 6: Seed
The treated area should be ready to seed once the plastic is off and any remaining weeds
have been removed. With effective site preparation, your native
wildflowers will be able to germinate and establish without excessive competition from
weeds. We hope you’ve learned enough to put solarization
to the test as you prepare areas for pollinator habitat in your home garden or on your farm! Let us know your experience in the comments. Subscribe to our channel to stay up to date
as we post new videos on pollinator habitat, bee research, and more. Visit our website at www.projecticp.org. Thanks for watching!

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3 thoughts on “How to Use Solarization to Prepare Areas for Planting

  1. Hello! Thank you for doing this great work! I was wondering about the option of not clearing the land of existing flowers. There are a number of wildflowers that are beneficial and appear naturally in my area. Is it possible to simply weed non-bee-beneficial plants and replace them with seeds from better wildflower species? Thank you!

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