It's Not Just "Dirt"

Every time you turn around, businesses are advertising potting soil at what appears to be a special low price. They say this bag is two cubic feet, this bag is such and such, and this bag is three yards and so on.

If you are like me, confusion is my middle name. What this all means is great if you know what is being offered, and sizes, of course, but I don't.

So I have studied and come up with a good potting soil you can blend yourself. The soil in which house plants and even starter inside beds have in them requires a little more attention than plants grown in the outdoors. It is most important in any artificial growing medium to have the right proportions to provide the right nutrients needed to sustain plant growth.

Ideally we should have sterilized soil to ensure freedom from soil-borne pests, diseases, and weeds. There are three methods to use to sterilize the soil:

  1. Formaldehyde Method - To treat soil in a flat 16 by 22 by 2 inches deep, mix 4 tablespoons for formalin (40% formaldehyde) with 6 tablespoons of water. Apply this outdoors. Moisten the soil, sprinkle the solution on it, mix the two well, and then cover with plastic for 12 hours. Air for another 24 hours (or until all odor disappears) before sowing seeds.
  2. Oven Method - Place a 4 inch layer of moist soil in a metal baking pan and cover with aluminum foil. Insert a candy or meat thermometer in the soil through the foil. Place the pan in the oven using low heat. When the thermometer has a reading of 180-200 degrees leave in the oven for another half hour. Remove the pan from the oven and let set for 24 hours.
  3. Pressure Cooker Method - Fill a canning type pressure cooker with 2 cups of water. Place a rack inside the cooker and stack shallow pans of soil (approximately 3/4 of an inch deep), leaving space for the steam to circulate. Heat and when 10 pounds are reached, maintain it for another 15 minutes. Remove from the stove letting it cool down. Wait 24 hours before using.

This general-purpose mixture can be used for most everything that have strong root systems:

  • 2 parts garden soil (the soil you sterilized)
  • 1 part peat moss or leaf mold
  • 1 part perlite, coarse sand, or bird gravel
  • 1/4 part bone meal or 1/8 part superphosphate
  • 1/2 part dry cow manure

For plants that need a soil with more organic matter, such as begonias and African violets, use the above mixture with double the amount of peat moss or leaf mold.

For plants such as azaleas, camellias, and gardenias, double the peat moss and dry cow manure and use superphosphate instead of bone meal.

For desert cacti and succulents, a moist, very porous potting mixture is essential. By volume use 2 parts of soil, 2 parts perlite, 1/4 part bone meal, and 1/2 part dehydrated cow manure.

Note: Purchased potting soil can be stretched by adding 1 part garden soil to every 3 parts purchased soil.

Barry Bishop
February, 1995