Pasteurize Your Own Compost

Reader Contribution by Nicole Caldwell
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By pasteurizing your own compost, you can ensure your seeds, seedlings, and garden beds will have the best chance possible to survive this growing season.

Those of you who have used last year’s compost for this year’s plantings have likely run into some of the same problems I have; notably errant seedlings sprouting up where they shouldn’t be (I’m looking at you, cherry tomatoes!), and mysterious “damping off” of your new seedlings — that is, one day they look good, the next, their roots have gone black and the plant has shriveled up to die.

Damping off is a horticultural condition caused by pathogens killing or weakening seeds and seedlings.Seeds that are infected with damping off will not germinate; and plant stems will shrivel — causing your seedlings to topple over and die. If you have waited an unusually long time for a particular seed to germinate, brush the soil away. If your seed is dark and soft, it’s got damping off. Sorry, you’ll have to start over.

This problem happens everywhere things grow, no matter where you live and there is absolutely no remedy once plants and seeds are infected. You can prevent damping off from happening one of several ways; though in my opinion the best way is by pasteurizing your compost before using it for potting soil.

Most people go out and buy sterilized potting soil, but that seems an unnecessary expense. If you’re an avid gardener, you’re likely to already have a compost pile. That dirt, while wonderful for mixing into your raised beds and garden rows, has the potential to have an overwhelming amount of micro-organisms that can harm your new seeds.

Some people solve this issue by baking their composted dirt in the oven—but in doing so, they sterilize everything (even healthy organisms you want to encourage!). So instead of doing that, pasteurize it. Pasteurization will heat your dirt to a level that destroys harmful organisms but leaves behind beneficial bacteria and microbes your seedlings will love.


Pre-heat your oven to 200 degrees Fahrenheit. Pour up to 4 inches of your composted soil into a large aluminum baking pan and put a meat thermometer in the center of the tray, deep into the dirt. Place the tray in the oven and keep an eye on the dirt’s temperature. Once the center of the dirt reads 160 degrees, bake for 30 minutes. Allow the dirt to cool thoroughly before using.

Photo By Nicole Caldwell

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