How to Sterilize & Reuse Potting Soil

Gardening is a rewarding way to reap the benefits of nature's bounty. While gardening can become expensive, there are some ways that you can save money and help recycle by reusing your potting soil. Sterilizing your potting soil and reusing it will rid the soil of harmful organisms or foreign seeds that may still be intact. When you sterilize and reuse your potting soil, it provides your plants with a healthier growing medium. Sterilize the soil one of two ways: using a microwave or an oven. Then use sterilized and recycled soil just as you would use any other soil.

Difficulty: Moderate

Instructions

Things You'll Need:

• Microwave-safe container
• Thick sealable plastic bags
• Oven-safe container
• Aluminum foil
• Meat thermometer

Oven Method

1. Moisten the soil thoroughly and preheat the oven to 200 degrees F. Ensure that the soil is wet, but not soupy, before placing it in the container you will use to heat it.

2. Place the moist soil in the heating container. Large plastic sealable bags going into the microwave should be filled with about 2 lbs. of soil. Containers that are going into the oven should be loosely filled with soil no deeper than 2 to 3 inches.

3. Cover the oven-safe container with aluminum foil. Place the dirt into the preheated oven.

4. Allow the center of the soil to reach 180 degrees F by measuring it with a thermometer intermittently. Once the oven-baked soil reaches this temperature, let it cook for 30 more minutes longer before turning off the heat.

5. Let the potting soil to cool inside the oven-safe container used to heat it, while keeping it covered in aluminum foil, until you're ready to use it.

Microwave Method

6. Place soil that is in a microwave-safe container in the center of the microwave. Plastic sealable bags for the microwave should be left open after being filled with potting soil.

7. Using the "full power" setting on your microwave set the timer for 3 to 5 minutes.

8. Check the soil's temperature to ensure it has reached 180 to 200 degrees F at its core.

9. Keep the soil covered or sealed if it is in a plastic bag. Allow it to cool inside the microwave before removal.

Tips & Warnings

• When using a microwave with a temperature probe, you can use a microwave-safe plastic dish with a lid. Poke two holes in the lid and place the probe in one while the other allows the soil to vent during heating. This will save you time instead of removing the soil from the microwave to measure its temperature.
• Ensure that you don't compact the soil too tightly when sterilizing it.
• You should also beware that sterilizing soil and dirt will give off an unpleasant odor.
• Avoid overheating your soil as this will kill off positive microbes in your potting soil and possibly poison your plants.

References

• Tip Nut
• Colorado State University

Resources

• tcpalm.com: Carol Cloud Bailey: Use microwave to sterilize potting soil