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I have had issues with either bacterial spot/speck or early blight (I was not able to determine which it was) or both on tomatoes. They have been grown in containers. I have about 100-150 galons of soil that could have been used to plant tomatoes and thus it could contain the bacteria/fungi. What would be the most efficient way to sterilize it?

I tried solar sterilisation but I think it likely causes more problems than it resolves. I am in central florida and soil sterilisation during summer is not really possible (unlike what some claim) due to the frequent rains unless one has some huge area to be used and glass on top (plastic simply gets ponds of water and/or water condensation on the bottom part of the plastic, both of which prevent the sun to efficiently warm the soil). At the same time, algea and who knows what develops in the still water on the plastic. Not speaking of ferral cats making this their excrement ground.

I also tried to put the soil in a container (20 gal tote such as from sterilite) and then pour in boiling water. This was not so bad but for thoe 20 gals i needed about 4 galons of water (to the dry soil), so it takes enormous amounts of time to boil all the water. Also, you basically create hot peat and need to find a way to remove the excess water from the soil.

Finally, I tried to put some soil in a bucket, wet it with water in and put it above fire. This I liked most because the soil was wet, it made sure that most of the soil did not experience temperatures above the boiling point. So i am thinking of buying some 20 gal steel bucket put some wood sticks on the bottom, pour in some 4 gals of water and then some burlap and on that the soil. This would be then sterilised by vapour. But this is huge amount of work (and plenty things to buy).

Does anyone have any better idea, or is this an overkill and I can use the possibly infected soil and only, say the top 5 inches use some uninfected soil? Chemical way also seems out of the question since chemicals for this purpose are only commercially available (and also i try to keep omri organic).

Thanks for suggestions.

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150 gallons at 4 litres per gallon makes over 500 litres or 8 domestic garbage bins of soil; this puts the project on the border between home gardening and small commercial, so you might get some help from the local agriculture extension office. Even a suggestion for concrete identification of the pathogen would help since then you have a clearly defined target. As it is you have to try treating for both.

Divide and conquer would be a good first approach. Seek out a black 70 litre garbage bin with close fitting lid and fill it with moistened soil, put in full sun and insert a long thick metal rod to reach to the middle and bottom of the bin. When you withdraw the rod the tip should be close to the temperature of the mass at that point which you can measure with a known good thermometer. There are some cooking thermometers with a long 12" probe which might suit for observations in the centre of the bin. In full Florida sun you should be able to get the mass pretty hot without melting the plastic bin. Several hours at over 100 F should take care of most bacterial and fungal spores. The enclosed bin would keep out the cats.

An alternate would be to get a lot of compostable materials (waste food, chopped straw, grass clippings) and mix together the compostables with the soil so that when the compost heats up it also heats the added soil.

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  • Thank you, that is a good suggestion. But I am not sure if it is going to work now, I would like to use the soil next week. But for summer solar sterilisation, it is a great idea. Do you have any other ideas to do it within a week? Thank you. – leosenko Mar 15 at 0:32

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