Question: We want to clear an area of lawn and replace it with a vegetable garden. I've heard of "solarizing"—can you tell me if this would be the best way to go and can we do it over the winter so we'll be ready to plant in spring?
Answer: Soil solarization is typically used to eradicate certain pests and diseases that inhabit the soil and harm plants. These include nematodes, verticillium and fusarium wilt, certain root rots, damping off and crown gall. Solarization also kills beneficial soil organisms, such as mycorrhizal fungi, but these grow back quickly after the tarp is removed. Solarization is sometimes used to destroy weeds, and it could be used to kill certain kinds of lawn, but not over the winter, because the method relies on heat. Solarization typically works on only the top six inches of soil, so if you have weeds or turfgrass with deeper roots, they may resprout.
To solarize an area, clear the area of any sticks or stones that would puncture a tarp and work the soil so that the surface is loose. Water the area, then cover it with a clear polyethelene or polyvinyl-chloride tarp, pulling the tarp taut against the ground. (These kinds of tarps are resistant to UV-rays, so they won't start to break down during the process. If you can't find them in your area, however, clear painter's plastic will usually survive four or five weeks in the garden.) Bury the edges of the tarp six inches deep, or secure them all the way around with stones or bricks to prevent them from being lifted or torn by wind. Patch any holes that occur promptly with duct tape. Solarization is best done during the hottest, sunniest time of year in your area. The tarp should be left in place for at least four weeks.
To kill your lawn before next spring, cover it now with several inches of cardboard or newspaper, then cover that with compost and/or chopped leaves. Water it well. In about two months, the grass should be dead. In the spring you can dig through what remains of the coverings (without removing them) and plant your garden.
Learn how to work with nature to create a sustainable garden in Gaia's Garden: A Guide to Home-scale Permaculture (Second Edition).
Learn about sheet composting, grow heaps, comforter compost and more in The Complete Compost Gardening Guide.
Get more advice and inspiration for replacing an area of lawn in How to Get Your Lawn Off Grass.