Sterilize Soil

Question: Some time back I read something in Horticulture about using a microwave oven to sterilize soil. I have not been able to find it again. Could you provide me with the information?

Answer: There is not set formula for sterilizing soil in a microwave oven because the amount of wattage varies with the brand. The wattage output can vary from 400 to 900 watts; the higher the output, the less time required for sterilization. The size of the oven also has some effect on exposure time.

One way to calculate how much time is needed for soil sterilizing in your oven is to see how long it takes for one cup of water to boil. Place wetted soil in the microwave oven and heat for the length of time it took the water to boil, then continue for one more minute. The soil will then no longer have microorganisms living in it. The high temperature and length of exposure necessary to kill all weed seeds would result in the breakdown of the soil’s structure. Therefore, sterilize your soil to rid it of microorganisms, but do not attempt to kill all weed seeds.