Definition - What does Air Prune mean?
In horticulture, air pruning of a plant's roots occurs when the roots that are exposed to air 'burn off' or die. Air pruning is a natural process for most plants because the roots that are exposed to the air serve no useful purpose.
MaximumYield explains Air Prune
Occasionally, roots from a plant reach the surface and extend beyond the soil. These roots will eventually die off because they are not receiving any nutrients. The sun can also air prune roots by heating and burning them off.
Air pruning is common in rock plants such as succulents where there simply isn’t enough organic matter present for the roots to completely grow in. Air pruning is also common with potted plants where the roots extend through the drainage holes and are exposed to air.
Likewise, air pruning occurs when plants are grown in fabric containers and the roots are allowed to grow through the fabric. In this case, air pruning is considered a benefit, as the plant is encouraged to continuously be growing roots, and therefore, yields. It is believed that root-bound plants can be prevented when grown in fabric containers due to the act of air pruning.
Because air pruning is a natural process, the gardener doesn’t really need to intervene and there is no harm done to the plant when they don’t.