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.
It is recommended as a good drainage rock. Packs down well.\nConcrete Mix â Made up of a sand and gravel mix. This is not the actual concrete mix that is bought it bags, rather it is used to add to bags of concrete.\nSlow 6 Pumice â Added to potting soild because of it's light weight.t is recommended as a good drainage rock. Packs down well.\nConcrete Mix â Made up of a sand and gravel mix. This is not the actual concrete mix that is bought it bags, rather it is used to add to bags of concrete.\nSlow 6 Pumice â Added to potting soild because of it's light weight.