How To Sterilize Potting Soil And Why You Should

Many people complain about their plant not growing properly or contracting a lot of diseases and pest infections despite having all the parameters set to the optimal conditions. In many cases, the problem lies not within their plants but in the potting soil itself.

Since soil can easily gather weed seeds, diseases, and pests, it’s always wise to sterilize the soil before planting it.

hand holding sterilized soil - Sterilize Potting soil kills weed seeds, pest and diseasesPin
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The problem is, sterile soil can be quite costly, and you’ll need to sterilize it again if it gets contaminated. For that reason, you need to know how to sterilize potting soil.

In this article, we’ll walk through a brief guide with various methods to sterilize the soil and why you should do it. 

How To Sterilize Potting Soil

There are various ways to sterilize potting soil. These different methods either use heat, steam, or chemical sterilization to get the job done.

The choice of the method relies on many factors, including availability, batch size, and personal preferences.

Why Potting Soil Sterilization is Critical for Your Plant

Sterilizing the soil has a lot of advantages that make it a critical step for the success of your gardening project, no matter how big or small it is.

Greenhouse with steam, soil preparation.Pin
Photo Credit: Instagram @highcroftnurseries

Here are some of the benefits include:

  • Sterilizing potting soil reduces the number of dangerous pathogens, harmful bacteria, pests, and fungi that can harm your plants significantly
  • Healthier plants by preventing the spread of diseases in your soil
  • Sterilizing the soil yourself saves you the costs of buying new sterilized soil
  • Reduce the future costs of maintaining the plant’s health
  • Boosts the cycle time of the plant
  • You’ll ensure the quality of the sterilization process
  • Some forms of sterilization might boost the release of nutrients like nitrates in the soil for better plant growth

Different Methods to Sterilize Potting Soil

Here are five different methods to get your potting soil ready for planting:

Sterilizing Chemically with Hydrogen Peroxide

Many chemicals can be hazardous and bad for your soil. However, hydrogen peroxide is easy to use and work for both large and small batches:

  • Prepare the 3% hydrogen peroxide mix by adding 1/2 cup of hydrogen peroxide for every gallon of water, then load the quantity in a sprayer.
  • Spread the soil on a plastic sheet for optimal coverage.
  • Spray the solution on the soil, and make sure you cover every part. (never pour the solution directly on the soil, as it’s too concentrated for the soil)
  • Allow the hydrogen peroxide to dry up before using the soil.

Related: Hydrogen Peroxide for Plants

How To Sterilize Potting Soil In The Oven

Using the oven to sterilize the soil is one of the most traditional ways to get the soil sterile. For that method, you’ll need an oven-safe container, a baking thermometer, and a roll of foil:

  • Lay some aluminum foil in the base of the baking pan
  • Add some soil to the container. (about 3″ to 4″ inches deep)
  • Cover the soil with extra foil with some poked holes for aeration, then add the thermometer inside the oven
  • Start the oven and set the temperature to about 175° to 185° degrees Fahrenheit (about 79.4 to 85 °C).
  • Keep the soil at this temperature for about 20 to 30 minutes. You can use the thermometer to make sure that the temperature doesn’t exceed that to avoid the release of dangerous toxins in the soil.
  • When the 30 minutes pass, remove from the oven and allow the soil to cool down without removing the foil.
  • Remove from the foil when ready to plant.

How To Sterilize Potting Soil In A Microwave

The easiest and quickest method for small patches:

  • Spray the soil with some water to make it barely moist
  • Fill a microwave-safe container with soil.
  • Cover the container with microwave-safe plastic wrap and poke some holes into it, or use a plastic container lid if it has holes.
  • Heat on the highest setting for 90 seconds for every 2 lbs of soil (1 kg).

Related: Can You Reuse Potting Soil?

Sterilizing with Hot Steam

Another easy method uses steam instead of raw heat:

  • Add some water into a deep and large steaming container.
  • Place a steaming rack inside the container.
  • Wrap the soil in foil and put it over the rack.
  • Bring the water to a boil.
  • Close the lid but leave a venting hole open to prevent the creation of pressure.
  • Leave for 30 minutes, then allow the soil to cool down.
  • Remove from the foil when ready to plant.

Soil Sterilization Through Solarization

Soil solarization heats up the soil by harnessing the power of direct sunlight.

  • Turn the soil you want to solarize
  • Collect and get rid of any dead plant material, plant roots, and other debris that could harbor pests.
  • Level and smooth the surface of the soil
  • Water the soil to a depth of 12″ inches. This allows the soil heating conductivity to increase.
  • Lay black plastic sheeting, or a garden tarp on the soil and anchor the edges of the tarp.
  • Wait 4-6 weeks before removing the plastic and planting.

If you have a pressure cooker, you can also use it to sterilize the soil mix. 

However, you have to use it with non-nitrated soil or before adding nitrogenous fertilizers because nitrates can explode under pressure. Also, make sure that the pressure in the pot isn’t too high.

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