Some of the common inorganic materials include sands, vermiculite, perlite, calcined clay, pumice and other mineral by-products. Adding organic amendments to a growing medium primarily improves its physical properties, such as increasing water-holding capacity and aeration, and decreasing wet weight. Particle size guidelines for organic and inorganic amendments. In addition to the requirements for particle size distribution and rate of incorporation, an organic amendment should be stable with respect to decomposition. This will eliminate nitrogen draft problems and reductions in volume of the medium during the growing season.
Sand is a common component of nursery growing media used for ballast weight.
This purpose may underestimate the potential impact it may have on the physical properties of the medium. Its use in a mix also requires an evaluation of particle size distribution. Sand use should be restricted to less than one-third of the mix volume, as it significantly increases the volume weight. The particle size guidelines given here are not to be used as rigid specifications, but as a help in evaluating and selecting materials for a container medium. They do not guarantee an ideal mix.