Silva Cell Facilitates Urban Tree Growth

DeepRoot Partners has created Silva Cell to address these problems by providing a framework for holding uncompacted subsurface soil that can support tree roots and manage the runoff from small storms. Each 48" x 24" x 16" (120 x 60 x 40 cm) fiberglass-reinforced polypropylene frame (there is no recycled content because of structural concerns) holds 10 cubic feet (0.3 m3) of soil and can support H-20 loading standards of 32,000 pounds (14,500 kg) per axle (the company does not recommend these under roadways).

Silva Cell uses six vertical posts, a base, and a top deck reinforced with galvanized steel tubes. The frames can be stacked up to three high before the top deck is attached and can be laid side-by-side to provide more soil volume. Root barriers and membranes are added to direct roots away from structures. The Silva Cell framework provides a space that protects soil and allows roots to grow naturally to support the tree’s overall health. “Depending on the site, trees need two cubic feet (0.06 m3) of soil per square foot (0.09 m2) of tree canopy,” said Graham Ray,executive vice president of Deep Root Partners. A typical 4' x 10' (1 x 3 m) streetscape contains about 20 cubic feet (0.6 m3) of soil, which limits a tree’s canopy to a 10–foot (3-m) diameter before it falls into decline. But a tree with a 20–foot (6-m) diameter canopy (see chart) actually requires 500 cubic feet (14 m3) of uncompacted soil, and finding that much quality soil in a crowded urban landscape can be a challenge.