Updated: March 3, 2020
If you want to make your own potting soil for house plants, you’ll need to learn how to sterilize it. Otherwise, you’re going to have creepy crawlies (a sophisticated horticultural term), A.K.A. bugs, running around your house.
Some people will tell you that homemade soil for house plants doesn’t need to be sterile. In fact, once the plants are established, they benefit from the soil organisms that live in unsterilized soil.
And it’s true. You’ll never get the very best possible plants with sterilized soil. But the problem is that creepy crawlies crawl out of unsterilized soil. Unfortunately, you’ll find them in unexpected places in your house. I don’t want that.
Related: Getting Rid of Gnats on Seedlings
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Other reasons to learn how to sterilize potting soil
There also are a couple of other problems with using unsterilized soil indoors. Sometimes it encourages damping off in new seedlings. Some people even sterilize potting soil for plants in their hoop house.
One more reason to sterilize potting soil: weed seeds are much less likely to sprout. This is especially true if you’re using homemade compost.
Sterile soil makes all these problems less likely.
Conventional wisdom says that to sterilize potting soil, you need to heat it to 180 degrees Fahrenheit for 30 minutes.
Most people believe that using an indoor oven for this is a bad idea. The odor from cooking the soil is not something you want in your house.
Plus, running the oven when it’s hot outside doesn’t make much sense if you’re paying for air conditioning.
Grilling soil
My solution is to use my gas grill. Outside the smell would quickly pass, and it wouldn’t heat up the house.
Here’s my step-by-step method for how to sterilize potting soil:
Time needed: 2 hours.
Sterilizing potting soil is pretty easy if you use a gas grill.
- Line a baking pan with tin foil.
You probably want to use an old pan so you won’t be eating out of a pan that had dirt in it.
- Fill the tin foil with homemade potting mix.
See the potting soil recipe below if you don’t have one you already like.
- Add a little water to the mix,
The object is to keep the soil moist.
- Cover the top of the soil with a second layer of tin foil.
This will keep everything in place and help keep the soil from drying out.
- Insert a meat thermometer.
Place the thermometer through the tin foil into the soil. You want to make sure it doesn’t touch the bottom of the pan because it won’t give you a true reading.
- Heat the soil at 180 degrees for 30 minutes.
Turn the grill on full blast and put the pan on top of the grates. You don’t want the temperature to go too much above 180 degrees Fahrenheit. Turn down the grill as the temperature approaches 180. Keep it as close to 180 as you can manage. If it goes much above 185, you could damage the soil.
That’s it, you’re done. Now you have sterilized potting soil.
My potting soil recipe
When I sterilize soil, it doesn’t seem to smell as much as most others say it would. Maybe that has something to do with the recipe I’m using:
- One-third screened compost
- One-third quality soil
- One-third clean sand
- A little perlite
The potting mix drains well, which is very important for container gardening. At the same time, it seems to hold moisture well, too. I tested it (both sterile and unsterilized versions) with green onions and organic mesclun mix salad.
Both turned out equally well.
Have you sterilized potting soil before? How did you go about it? Let us know by commenting below.
Related articles that might interest you:
- Which Seed Starting Mix is Best?
- I Shopped for Hoop House Kits. A Review of the Three I Considered
- Soil Blocks Vs. Paper Pots.
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