Potting soil not only provides a place for container plants to set down their roots, it also must provide adequate nutrition, drainage and moisture holding capabilities for the plants to thrive. Soil straight from the garden isn't suitable as a potting soil. It is often filled with weed seeds and disease organisms that can plague any plant planted in it. Making a homemade potting soil that is suitable for most plants requires combining the proper, sterile components together to create the best soil environment possible.
Sift compost or garden soil through a piece of window screen material. Remove any roots, uncomposted chunks of material and rocks from the compost or soil, keeping only the fine textured material.
Place the soil or compost into a roasting pan and sprinkle it with water until it is evenly moist. Cover the soil with a sheet of foil and stick an oven thermometer through the foil and into the soil.
Place the soil in a preheated 200 degree Fahrenheit oven. Bake until the soil reaches an internal temperature of 140 to 180 Fahrenheit, then maintain this temperature for 30 minutes. Remove from the oven and allow the soil to cool to room temperature.
Mix the sterilized compost or soil with one part peat moss, which helps maintain proper moisture levels in the mix, and one part sand or vermiculite, which prevents the mix from becoming soggy or waterlogged.
Mix a complete fertilizer into the potting soil at the rate recommended on the fertilizer bag. Alternately, add 1 ¼ cup agricultural limestone, 1 cup 5-10-5 analysis fertilizer and ½ cup superphosphate fertilizer per every two bushels of homemade potting soil.