In the formal language of economics, X and Y are substitutes if the demand for X increases when the price of Y increases, or a positive cross elasticity of demand.
Potting mix is the material that goes into a garden pot before you put seeds and plants into it. 1  It keeps the plant in place. 2  It holds water for the plantâs roots to soak up.  It contains nutrients that feed the plant.
Either soil-based or peat-based potting media can be made at home by combining individual ingredients. Recipes given here are measured in gallons for primary ingredients and in teaspoons and tablespoons or ounces and grams for smaller ingredients.