Making potting soil from scratch is an excellent way to learn about the various ingredients that are used in soil mix and the specific purpose of each. After you become familiar with the ingredients, you can experiment to find exactly the right mixture for the particular needs of your plants. The recipe that follows is an all-purpose soil mix that Martha has used frequently.
When mixing, start with a clean container, such as a galvanized washtub, large enough to hold all of the ingredients. Use a scoop or small pot to measure ingredients. It is very important that you wear a surgical mask over your mouth and nose while you're working, so you won't inhale dust particles, and that you lightly spray the mixture with water. (Don't overspray, or you'll end up with mud.)
Mix the ingredients together thoroughly and store them in covered, galvanized containers or plastic trash cans. Don't make too much soil mix at once -- over time, the organic content can spoil.
- 3 parts peat (screened). Peat is a natural organic material that helps soil retain air and moisture by increasing pore space. Aged, pulverized bark can be substituted.
- 2 parts perlite (horticultural grade). Made from volcanic material, perlite is a light aggregate that provides aeration, increases drainage, and absorbs little water.
- 2 parts topsoil (screened and sterilized). A complex mixture of minerals, organic materials, microorganisms, and pores filled with air and water. You can purchase sterilized topsoil, or sterilize your own from screened soil from your garden. To sterilize soil, place it in a shallow pan on your outdoor grill, until temperature of soil reaches 160 degrees F to 180 degrees (use an old meat thermometer).
- 1 part vermiculite. Vermiculite is derived from mica; it provides aeration and, unlike perlite, absorbs water.
- 1 part No. 3 coarse sand (not beach or play sand, which is too fine). Helps with drainage and aeration of soil; adds weight to keep pots stable.
- 1/4 part charcoal (horticultural grade). Keeps soil slightly alkaline and absorbs any dissolved salts in the soil; helps provide aeration and drainage.
- 1 cup bonemeal. Adds nutrients and phosphorus, necessary for good root and flower formation.
- 10 tablespoons Dolomitic lime. Helps balance pH of mix.
- 14-14-14 Osmocote (follow package instructions to determine amount). A time-released fertilizer; adds essential nutrients for good plant growth.
Potting Soil Mix How-To
Mix ingredients thoroughly, and transfer to covered storage container. Lightly moisten mixture when ready to use.