How to Sterilize Seed Starter Mix


Depending on the plants you want to grow, starting seeds can be easy or a little more challenging. Aside from planting seeds to the right depth and keeping the soil moist, you also want to make sure you are using a clean soil mix to avoid fungi and bacteria that may prevent your seedlings from thriving. To sterilize seed starter mix, you'll need to prepare your materials ahead of time for cooking the soil and then be ready to plant once the soil has cooled down.

Step 1

Wet your seed starter to make it evenly damp so it clumps in your hand but does not stay clumped when you open your hand. Fill your baking pan evenly with the damp seed mix 3 inches deep or less.

Step 2

Place aluminum foil over the pan to cover it, and press the foil onto the pan edges to seal tightly. Stick a baking thermometer into the center of the foil and push it down into the seed mix.

Step 3

Set your oven to preheat to 180 degrees F, and make sure it is at this temperature before putting your pan into the oven. Adjust the pan as needed so you can see the thermometer easily.

Step 4

Wait for the thermometer in the pan to read 180 degrees by checking it every 5 to 10 minutes. At the point that your seed mix is at 180 degrees, set the timer for 30 minutes, and leave the mix to cook.

Step 5

Take the mix out of the oven after 30 minutes, and set it aside to cool thoroughly. Use the seed mix right away once it is cool to get the benefit of the freshly sterilized mix.

Tips and Warnings

  • Cooking your seed starter mix at too high a temperature can break down the nutrients in the soil, so don't try to raise the temperature to shorten the cooking time.

Things You'll Need

  • Seed starter mix
  • Water
  • Baking pan
  • Aluminum foil
  • Baking thermometer
  • Timer


  • "Success with Seeds"; Chris Wheeler and Valerie Wheeler; 2004
Keywords: sterilizing seed mix, cleaning seed starter, seed starter mix

About this Author

Margaret Telsch-Williams is a freelance, fiction, and poetry writer from the Blue Ridge mountains. When not writing articles for Demand Studios, she works for as a contributor and podcast co-host.