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How to sterilise potting soil

Updated February 21, 2017

Sterilising potting soil before planting or transplanting your seeds or plants ensures they grow healthy and beautiful. The sterilisation eliminates fungi, bacterial diseases and destructive bugs that may be in the soil. You can sterilise your own soil at home in your oven.

Turn your oven to a low temperature of about 80 degrees C (180F).

Add peat moss, manure or compost to your soil before sterilising it. Make sure the soil mixture is moist, but not wet. You should be able to make it into a ball with your fist and the ball should fall apart a little when you open your hand.

Place the soil on a metal baking tray or any container that isn't plastic. Spread the soil evenly out with your hands, making sure that it isn't deeper than 10 cm (4 inches).

Cover the container very tightly with aluminium foil. Stick a meat thermometer through the foil in the middle of the container until it enters the middle of the soil.

Keep an eye on the thermometer by checking it occasionally until it reaches 80 degrees C (180F).

Keep it at this temperature for about 30 minutes. Make sure it doesn't go over 95 degrees C (200F). Check the temperature often to see if regulating the temperature set on the oven is needed.

Remove the soil from the oven and allow it to cool at room temperature.

Tip

You can buy sterilised potting soil, which is more expensive than the do-it-yourself method and still may contain harmful fungi, disease or insects that have developed in the bag during transit.

You can also sterilise soil using a microwave by heating it on a high setting in a closed plastic container. You have to poke a hole in the lid for ventilation and keep the temperature at 80 degrees C (180F) for 20 minutes using this method.

Warning

The soil leaves an offensive odour while cooking. Make sure your house is well ventilated when sterilising soil with this method.

Things You'll Need

  • Potting soil
  • Roasting tin
  • Aluminium foil
  • Meat thermometer
  • Oven
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