How to Sterilize Seed Starter Mix

Sterile soil helps ensure healthy seedlings.

Starting your own plants from seed is more economical than purchasing seedlings from a nursery. You also have a greater choice in plants and varieties if you choose to start from seed. Seed-starting potting mixes are preferred over regular garden soil because they are better draining and made from sterile components such as sterilized compost, peat moss or vermiculite. You can sterilize homemade or reused seed-starting mix so it doesn't harbor weed seeds or disease organisms that can kill young seedlings.

Things You'll Need

• Compost or soil
• Roasting pan
• Foil
• Food thermometer
• Peat moss
• Vermiculite or perlite

Instructions

1. Sift through the compost or garden soil prior to sterilizing. Remove any un-composted items or roots and break up any large chunks of soil.

2. Fill a roasting pan with the sifted soil or compost to a 3- to 4-inch depth. Sprinkle water on the soil until it is moist but not soggy.

3. Cover the roasting pan with aluminum foil. Poke a food thermometer through the foil near the center of the pan and into the soil beneath.

4. Place the foil into a preheated, 250 degrees F oven. Heat the soil until the thermometer reads 180 F. Maintain this temperature for 30 minutes.

5. Remove the soil from the oven and allow it to cool to room temperature. Mix with one part peat moss and one part vermiculite or perlite before using to start your seeds.

Tips & Warnings

• Perlite, vermiculite and peat moss are sterile if they have not been used before. If they have been used, sterilize them the same way you do the soil.

• Use disposable foil roasting pans if you do not wish to bake soil in the same pans you use for food.

• Store unused potting mix in a sealed container so it remains sterile.

• Dirty pots and planting tools can spread disease to otherwise sterilized seed-starting mix. Sterilize these in one part bleach mixed with nine parts water to avoid reinfecting the potting mixture.

References

• Oregon State University: Make Your Own Potting Soils