How to Sterilize Composting Soil

Compost is a rich soil amendment that often makes up at least a third of many seed starting mixes and homemade potting soils. While the high temperatures in the compost pile kills many weed seeds and disease organisms, some may still survive.

Sterilising the compost before use in soil mixes will neutralise any remaining harmful elements. Sterilising also allows you to reuse compost mixes with no worries of spreading plant diseases to your new plantings.

Check the compost for any large, uncomposted elements, such as twigs or chunks of wood. Remove these and return them to the compost pile to finish breaking down.

Preheat the oven to 93.3 degrees C. Move the oven rack to the lowest position inside the oven.

Fill a roasting pan with compost to a depth of 4 inches. Cover the pan with foil, crimping it around the edges for a tight seal.

Stick an oven thermometer into the soil. Push it through the foil covering into the centre of the pan.

Cook the compost until the thermometer reads 180 degrees. Continue cooking for 30 minutes at this temperature.

Remove from the oven and allow to cool before using in your soil mixes. Keep covered with the foil until you are ready to use it so it remains sterilised.