An understanding of the physical, chemical and biological characteristics of a growing media can improve plant growth and your bottom line. In this article we look at the physical characteristics of growing media.
Air Filled Porosity - AFP.
AFP is the percentage of the growing media occupied by air after the media has been saturated with water and allowed to drain. More air in the media will improve root growth, but a higher AFP may require more frequent watering and consequently nutrient leaching may be increased. Container depth has a significant effect on AFP as, in shallow containers, the AFP is reduced due to the greater proportion of media occupied by the saturated media in the bottom of the container. AFP will also decrease during the growing cycle, but this can be compensated, to a degree, by the increased ability of the plant to extract water from the growing media, reducing the amount of pore space occupied by water. A range of 13-30% AFP is considered to be acceptable under EcoHort guidelines for general nursery stock.
