old last growing season's potting soil, possible reuse - Ask Extension
We have much used potting soil from raised beds or different sized single pots and was told you could microwave it or pour boiling water over it to s...
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old last growing season's potting soil, possible reuse #924869
Asked February 21, 2026, 5:33 PM EST
We have much used potting soil from raised beds or different sized single pots and was told you could microwave it or pour boiling water over it to sterilize it- then reuse it the following growing season. However, feel would be very time- consuming due to the volume. Most of the pots contained vegetables or herbs. Is there any other solution. ? There were no problems re: bugs or fungus we were aware of.
Anne Arundel County Maryland
Expert Response
We don't recommend attempting to sterilize the media; it's impractical in this situation, as you noted, and it won't stay sterile for long, as airborne fungal spores and other microbes can always recolonize it once it's put back into use. (If you had experienced problems with suspected root or wilt diseases last year, then we'd suggest emptying the pot instead, cleaning it, and using fresh mix for new plants.)
To reuse potting mix, you can add compost to it (as much as 50% by volume) or add fresh potting mix in the same proportions. This will help increase porosity for good drainage, and compost in particular can reduce the risk of soilborne diseases by introducing beneficial microorganisms that help roots resist infection. This coming season, fertilize the new plants regularly as the old potting soil will have been largely depleted of nutrients, and nutrients from compost are slow to be released and will not be sufficient by themselves.
Miri
To reuse potting mix, you can add compost to it (as much as 50% by volume) or add fresh potting mix in the same proportions. This will help increase porosity for good drainage, and compost in particular can reduce the risk of soilborne diseases by introducing beneficial microorganisms that help roots resist infection. This coming season, fertilize the new plants regularly as the old potting soil will have been largely depleted of nutrients, and nutrients from compost are slow to be released and will not be sufficient by themselves.
Miri
