Texture affects water retention and, consequently, air porosity. Smaller pores present higher resistance to water flow, which in turn increases water-holding capacity. The size of the particles and their distribution determine texture. Clay is comprised of smaller particles, while sand is comprised of larger particles. Mixing components of varying particle size dramatically affects air porosity.
Mineral soils tend to have smaller particles.
When mixed with organic components, which usually are comprised of larger particles, soil lodges between the larger particles, reducing air porosity and increasing water retention. When various-sized particles are mixed, smaller particles lodge in the spaces left by larger particles, reducing pore size. Aeration and Water Retention One of the challenges floriculture growers face is balancing aeration and water retention, especially when growing crops in small containers. Increasing aeration decreases water retention and vice versa. Some growers believe that this challenge can be met by finding the ideal, all-purpose growing mix.