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So this year, a lot of my inside potted plants got attacked by powdery mildew and other afflictions. All affected were previously given soil that I sifted from the composter that is on the porch of our building. Likely, some people in the building previously discarded sick plants there, not knowing the spores may survive quite a while.

I was thinking in general, when taking soil from outside to use for potted plants, would it help to let it dry and then heat it to say 60°C (140°F) so that a lot of various pathogens perish? I think some diseases may not even present in outside plants that get enough sun, but may still hurt the ones in the inside.

Tomáš Zato
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  • I heated potting soil in an oven by accident years ago. Noticed it pretty soon because of the bad odor. Is it worth stinking up the house? – blacksmith37 Aug 06 '22 at 20:18
  • Well the odor will probably depend on temperature. If you go over boiling point, lot of things will start to decompose and that can get nasty. But 60-70 celsius is generally agreed upon temperature that kills most things if sustained long enough. – Tomáš Zato Aug 06 '22 at 21:50
  • Check which plants have the powdery mildew, each disease doesnt affect all plants. – Polypipe Wrangler Aug 08 '22 at 07:15
  • @blacksmith37 So I tried it already with a large amount of soil in the oven. The stench was short lived and not so bad. I cannot say if it was worth it until I see some results, but the whole operation was not difficult. – Tomáš Zato Jan 22 '23 at 02:06

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Yes, heat will kill Powdery Mildew including spores according to this paper.

Powdery mildew spores and mycelium are sensitive to extreme heat and sunlight, and leaf temperatures above 95°F may kill the fungus.

To destroy all organisms you will have to use an autoclave

Gyrfalcon
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