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How to Sterelize Home Made Soil-Less Medium?


Posts: 14074
Joined: Tue Jan 01, 2013 8:32 am
Location: Hawaii, zone 12a 587 ft elev.

if you are making the mediums from purchased peat moss and perlite out of the bag. The ingredients are already sterile and do not contain weed seeds. Make sure the peat moss was kept dry. Mold can grow on peat moss in bags if they get soaked for a long time.

If you are reusing soil less mix that is another story. Commercial nurseries will sometimes get a steam sterilizer or Soil King sterilizer to sterilize the soil and kill weed seeds and diseases.

If you do it at home, it can be done in an oven but it is a very stinky proposition. I did it once and never again.

Usually what I do is take used soil mix from my pots as long as the plant that was in it was healthy and use in my yard. I wash the pots with a scrub brush and bleach, rinse it out well and use new mix in the pots

My formula for potting mix is
one part perlite
one part peat moss
osmocote slow release fertilizer one handful per 5 gallon bucket

If you make mix in quantity it is cheaper to buy the individual parts 3.8 cu ft peat moss 4 cuft perlite
50 lbs osmocote or other controlled release fertilizer from an agricultural supply.

The mix can also be customized for cactus and succulents since you might want a drier mix.

When I want better drainage and for more acidic plants I replace the perlite with cinder. I also do that when I cannot find perlite. Cinder will make the pots a lot heavier.

I don't use vermiculite or compost in potting mixes because they hold too much water for me. Some people like to add topsoil to their potting mix. It is only a small amount sometimes only a couple of shovel fulls. It will make the mix heavier and hold more water. If you don't add a lot you may not have the problem of contraction in the pots and it does add some soil bacteria to an otherwise sterile mix.

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Super Green Thumb
Posts: 25279
Joined: Sun Feb 15, 2009 6:04 pm
Location: TN/GA 7b

Why are you trying to sterilize your mix? and to eliminate what? germs/micro-organisms, weed seeds, insects, nutrients? (We say seed starting mix is "sterile" because it has no nutrients).

I make my own mix from mushroom compost, coconut coir (peat moss substitute), rice hulls (perlite substitute). The mushroom compost comes in a sealed bag, but I don't know that it is "sterile" depending on what you mean by that. It clearly has some mushroom spores in it, since they sprout. I don't sterilize anything. But the potting mix goes in the ground with the seedlings and is not re-used.

I agree with imafan re the oven. I did that too. The first time I tried making my own potting mix, I was using my own homemade compost. But too many creepy-crawlies came in with the compost, that I don't mind in the compost pile, but I didn't want in my house. So then I tried baking the compost in the oven. Stank the house up! I won't do that again, either. That's why I use the mushroom compost now.

And I never put garden dirt in, but you specified soil-less medium, so you weren't planning to do that.

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