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Home  > Question of the Week

Question of the Week

Permalink I have nematodes in my pepper and tomato container soil. Is there a way to purify the soil?

Answer: The ATTRA publication Nematodes: Alternative Controls discusses many methods for managing nematodes, including using heat through steam and solarization. It is available at

Below is an excerpt from a Start Seed and Transplants in Sterilized Soil, by Laura Pottoroff, on using an oven to sterilize small amounts of soil:

"Oven Method—Spread soil not more than four inches deep in non-plastic containers, such as seed flats, clay pots and glass or metal baking pans. Cover each container tightly with aluminum foil. Insert a meat or candy thermometer through the foil into the center of the soil. Set the oven between 180° and 200° F. Heat the soil to at least 180° F; keep at this temperature for 30 minutes. Do not allow the temperature to go above 200° F. High temperatures may produce plant toxins. After heating, cool, remove containers from the oven and leave aluminum foil in place until ready to use. The heated soil will give off an odor." (1)

If you are interested in doing solarization, there are a few principles that seem to increase its effectiveness:
1. The plastic that you use should be clear.
2. You should apply the sheeting during hot weather.
3. Effective solarization requires good movement of heat into the soil. This is aided by high levels of soil moisture, so the soil should be irrigated before the plastic is laid down. Air gaps between the plastic and soil should be minimized as they inhibit heat transfer into the soil.
4. To prevent the plastic being lifted by wind, and to reduce the leakage of heat, the edges of the sheet should be buried.
5. In order to kill the organisms, and weed seeds, you may need to keep the soil covered for two weeks.

Both of these sterilization methods will kill virtually everything in the soil. In order to build up a healthy soil community again, I recommend adding Mycorrhizae inoculant after the sterilization process. Mycorrhizae are the symbiotic fungi that surround and penetrate plant roots. Studies have shown that these organisms can aid plants in conditioning the soil, as well as help in disease prevention after the sterilization is complete.

1) Pottorff, Laura. Start Seed and Transplants in Sterilized Soil. Colorado State University Extension Service.



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