Water relations of nursery potting-media

The available water-holding capacities (AWHC) of different potting-materials varied widely; coarse sand has a very low AWHC, and peat moss, sawdust, poppy straw and brown coal each have a high AWHC. The AWHC determines the length of time taken for plants to wilt, except in the case of peat moss and pinebark. Much of the available water in peat moss is rapidly lost through evaporation and easy exploitation by the plant. Pinebark, because it resists water loss through evaporation, and because its available water is not readily accessible to the plant, is able to maintain plants unwilted for a longer time than peat moss despite its lower AWHC. The AWHC and wilting-time of mixtures of 2 potting materials can be predicted from their individual properties.