Root tips penetrate the geotextile wall and base, unimpeded, and grow out into the surrounding soil. The fabric allows the root to expand until it reaches a diameter of 3mm, when the fabric stops giving and the root is successfully restricted.

After 16 years of continuous trials, across a broad selection of amenity trees and shrubs, the 3mm restriction has been proved to be the most effective size to block the phloem vessels, in the outer cambium layer of the root, while allowing the xylem vessels, closer to the core of the root, to continue to function outside the Fielder.

The immediate benefit of this continuous cycle of root restriction to 3mm is a reduction in the apical dominance within the root, leading to the profuse growth of vigorous lateral roots within the Fielder.

Roots outside the Superoots Fielder, 3mm at the point of restriction, become limited in length but they continue to source water and nutrients, along the xylem core vessels.

Roots inside the Superoots Fielder, swell and form energy nodules (see image) as carbohydrate moves down from the crown in the phloem vessels into the root system, and is blocked by the Fielder.

The benefit of these starch-charged nodules is that this readily available source of energy promotes an almost immediate development of roots from behind each nodule after transplanting.

Any escaping root, where the root is not sufficiently restricted by the fabric, becomes dominant. The phloem is not blocked so energy is lost into this root and considerably less branching occurs within the rootball.

This emphasizes the need to use a Superoots Fielder made of fabric specially designed to restrict roots, rather than inferior root control bags made of engineering fabrics. These bags restrict some roots, but are not consistent and allow too many root escapes.