Whether you are preparing for spring seed starting or just want to plant a few containers of flowers or herbs, potting soil is a necessary element. Purchasing all your potting soil can get expensive, especially if you have a lot of planting to do. Making your own sterilized potting soil is cheaper and requires minimal effort. And you can be sure it's sterile and weed-free. Make your own mix two or three weeks in advance of needing it, so it is ready come planting time.
Fill a roaster pan with a 3- to 5-inch layer of compost, either store-bought or from your own compost heap.
Cover the roaster pan with aluminum foil, and place a food thermometer through the foil and into the compost.
Place the pan in a preheated 250-degree Fahrenheit oven. Check every ten minutes until the thermometer reaches 180 degrees, then let cook for 30 minutes.
Mix 1 part of your sterilized compost, 1 part sand and 1 part peat moss. Break up any large clumps while mixing, and combine thoroughly.
Store in 5-gallon buckets until the potting soil is needed. Place the lids on each bucket securely so the soil mix remains sterilized.