Larger particle size also contributes to a greater percentage of aeration porosity than water-holding porosity. In addition, particle size of the media mixture influences media porosity. Because media particles are various sizes, the combined volume of two or more types of media is less than the sum total of the initial volumes. Large pore spaces created by large particles are filled by smaller particles when mixed together. Mixtures containing both large and small particles have less aeration porosity, or large pore space, than media composed of only large particles.
Particle attributes Particle attributes influence the ratio of aeration to water-holding porosity.
Chemical and physical media attributes affect particle shrinkage, breakage, and compression. Decomposition, compaction, and breakage of media alter the original media porosity. Saturation of available pore space forms a perched water table. Smaller pore space reduces media drainage as water is held more tightly in the smaller pores. As the root system of the plant grows, large pore spaces become filled, decreasing media aeration porosity.