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.
In place of peat moss, perlite and vermiculite (the three leading ingredients in bagged potting soil), you can simply combine your best soil with cured compost, leaf mold, rotted sawdust (from untreated wood) or a long list of other organic ingredients.n place of peat moss, perlite and vermiculite (the three leading ingredients in bagged potting soil), you can simply combine your best soil with cured compost, leaf mold, rotted sawdust (from untreated wood) or a long list of other organic ingredients.