Sterilizing soil-less mix with boiling water and H202

outsiders71(z5b)March 14, 2008

I have an open bag of perlite sitting in my barn that I want to use for this season's veggies.

I'm trying to evade using the microwave/oven to sterilize the soil. After I get my soil-less mix together, could I just throw boiling water onto the soil and stir it? Or add a little hydrogen peroxide to the boiling water to sterilize it?

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Why do you think it necessary to "sterilize" this soilless mix? Keep in mind that pouring boiling water, and/or H2O2, will also kill any of the good bacteria there might be as well as the few disease pathogens that might, possibly, be there.

    Bookmark   March 14, 2008 at 7:56AM
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I think that sterility in seed starting mixtures is pretty much a myth. If the open bag of perlite is dry, very few microorganisms will be living on it, and certainly not the group of fungi that cause damping off. They need lots of moisture. On the other hand, a bag of potting soil left outside to turn green and grungy would be teeming with those guys, and you'd have a reason to reduce their numbers with heat.

Hydrogen peroxide kills bacteria and some fungal spores, but actively growing fungi survive exposure at low concentrations.

If you keep moisture at the right level and use small containers for seed starting, I see no reason not to use your perlite right out of the bag. The dry vermiculite I'm adding to my seed-starting mixtures has been open for 3 years. I've been growing little greenies for a month, and haven't seen the first sign of damping off.

Here is a link that might be useful: my website

    Bookmark   March 14, 2008 at 8:05AM
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For indoor seedlings, I pour boiling water twice thru all my soilless medium. This has reduced or eliminated the incidents of damping off, fungus gnats, and mosses.

    Bookmark   March 14, 2008 at 8:47AM
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Pour perlite plus a couple gallons of nearly boiling water into an insulated cooler and let it sit for 45-90 minutes or so. You'll get a thorough pasteurization depending on where the temperatures stabilize.

Pasteurization is ideal for this purpose because it won't kill off any the beneficial thermophillic bacteria (acetymocytes? - can't remember how to spell their name for crap!) that you normally find in healthy compost...

    Bookmark   March 14, 2008 at 2:53PM
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Damping off and Fungus Gnats are both the result of someone being way to kind, they think, to their seedlings or plants, overwatering. Water just enough, not too much, and neither will be a problem.

    Bookmark   March 15, 2008 at 8:08AM
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digdirt2(6b-7a No.Cent. AR HZ8 Sun-35)

Agree. Damp-off is caused by the grower, not by the soil-less mix. It is caused by excessive moisture and inadequate air circulation around the seedlings.

And the beneficial microbes in compost, if added to your seed starting mix, will actually kill the fungi in the mix that can lead to damp-off when proper conditions are not maintained by the grower. Many of us who grow from seed routinely add compost to our mix - both starting and growing-on mix - with no problems (and with bigger and healthier seedlings as pictures in several posts can attest ;). Indeed most soil-less seed starting mixes on the market already contain some compost.

Sorry, but flushing seed starting mix with water - boiling or otherwise - may make the grower feel better but it merely drains out whatever nutrients it might have contained in the mix.

But do your own test comparison trying some each way - always room to learn something new. ;)


PS: It's fine to use your perlite as is. It is an inert material.

    Bookmark   March 15, 2008 at 1:35PM
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