Originally Posted by Will Heath

EDIT:

Correction as pointed out by Bill Struhar.

Vance's design is intended to combine excellent drainage with air pruning of roots. The root tips that reach the air through the screen stop growing, which allows resources to be redirected to other roots deeper within the soil. Thus, the ramification which occurs due to growing in a screened container does not occur at the screen, but rather in the interior (where we want them).

Will Heath