Sterilize Your Seed-Starting Soil

Mar 23, 2024

Are you getting ready to start some seeds for your spring and summer gardens? Maybe you have some seed starting mix leftover from previous years. It is important to use disease-free soil for starting your seedlings in order to give them the best and strongest beginning and to help prevent damping off. 

If a gardener is unsure whether their seed starting mix was free of diseases and weeds, one option is to sanitize the soil with heat. In the past we may have sterilized soil in the oven, but according to the LSU AgCenter, a quicker way to do it is in the microwave! Here's how.

Put seed starting medium in a microwaveable container. It could be a resealable, microwaveable plastic bag, or a glass dish. Make sure your soil has about 50% moisture. It will feel damp, but it won't drip liquid. If you squeeze a handful, it will form a loose clump that is easily broken up. Place it in your microwave and cook it for about 90 seconds in a 600-watt
oven. You want it to be at about 200 degrees Fahrenheit. Use a thermometer to verify the temperature and continue heating it in 30 second intervals until it reaches the correct temperature.

After it has cooled, you may plant seeds or start cuttings in it right away, or you may store it sealed up to a year. 

Obviously this won't treat a lot of soil, but you don't need much to start seeds. If you need a lot of soil, you may want to purchase a new bag or bale of commercial seed-starting mix.

For more gardening information, check out the Master Gardeners of Inyo and Mono Counties webpage at: .