Q. Is there a way to sterilize soil other than baking it in an oven? I like to recycle my old soil from containers. I first sift the soil and then store it in large plastic cans. Unfortunately, the weed seeds are not killed when stored for a year or so. Do you have any other suggestions?
A. A household oven isn’t a very practical method of sterilizing soil. I don’t think it was ever a popular or widespread practice. Storing soil for a year or more in the dark isn’t very effective either. Soil needs to be heated first to effectively kill the weed seeds, soil insects and other soil pathogens. The sun is a far more common method of sterilizing soil. This process is called soil solarization.
Soil sterilization is a sensible solution for large areas or small quantities of soil. Black plastic or a commercial tarp is the only equipment necessary. The used soil is place in a pile, pre-moisten, and then cover it sealing the edge so the moisture doesn’t escape. You should select an area that gets eight to ten hours of direct sunlight a day. It should bake for six to ten weeks June through September. The weeds seeds are killed as the temperature rises, converting the moisture to steam. You will control a fair amount of the problems but not one hundred percent. You could accomplish this in a plastic container but I think covering the soil is more effective. Once it’s been sterilized and aired out, you can store it in seal container indefinitely.
Another way to control weed seeds around desirable plants in containers or in the ground is with pre-emergent herbicides. There are granular pre-emergent products available such as Pre-Seeder Weeder or Preem. I’d ask the nursery professional at your favorite garden center for a recommendation. Weed control in a landscaped area is best accomplished with two to three inches of mulch. Mulching prevents the weeds from germinating as it blocks the sunlight from reaching the soil Weed Block and similar products are available; however keep in mind every couple of years you need to remove the old mulch and refresh it will new. The old mulch can be recycled and used as a soil amendment. In summary there are many other desirable methods of sterilizing soil available other than using your oven.
Buzz Bertolero is Executive Vice President of Navlet’s Garden Centers and a California Certified Nursery Professional. His web address is www.dirtgardener.com and you can send questions by email at dirtgarden@aol.com or to 360 Civic Drive Ste. ‘D’, Pleasant Hill, Calif. 94523 and on Facebook at Facebook.com/Buzz.Bertolero
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