Soil solarization is an environmentally friendly method used to rid an area of pretty much everything: weeds, fungal and bacterial pathogens, and nematodes, in particular. Solarization is particularly effective against the pathogens that cause fusarium wilt, verticillium wilt, root rot, blight, tomato canker, and crown gall disease. It is also used to eliminate a lawn and prepare it for more drought-resistant varieties of plants.
To prepare an area for soil solarization, it must be smoothed flat and free of dirt clods and visible weeds. Solarization works far better on level areas than on hillsides, but sun exposure is critical for the process to be effective. Shady areas are not suitable.
Basically, soil solarization covers an area with clear or white plastic and lets the sun cook everything to death. Now, when I say covered, I mean completely. No cracks, no bubbles, no loose edges. If gophers, ground squirrels, or birds are a problem in your area, this can be difficult.
Here are the steps to use for effective soil solarization:
NOTE: Black or colored tarps should not be used unless you live in a cooler, coastal area. In this case, a black tarp will prevent weeds from growing during the early part of the process and the tarp will need to be left on longer than normal. When selecting the sheeting material, heavier is generally better:
Using a double layer of plastic, separated with plastic bottles or PVC pipe, can increase the effectiveness of solarization. This has been shown to increase temperatures by 2-10°F.
If it is done properly, the heat of the sun should reach 140°F, killing pathogens and weed seeds, without the use of chemicals. Another benefit of soil solarization is that it speeds up the breakdown of organic matter, making all the nutrients bound up in various life forms available to new plantings. Plants grown on solarized soil tend to grow bigger and faster, as a result. Of course, this process also kills earthworms and beneficial soil microorganisms.
Soil solarization can also be used on planting containers and in raised beds that have become infested with undesirables. In this case, use a double layer of plastic and place the container in the sunniest place you can.
Once solarization is complete, either remove the plastic or leave it in place, as a mulch. Personally, I don’t recommend using plastic in the garden, but it’s your call. When removing the tarp, you will want to disturb the ground as little as possible to avoid planting newly arrived weed seeds.
You can grow a surprising amount of food in your own yard. Ask me how!