One of the most common questions posed when beginning an urban forest project is: how wide do tree roots grow? The answer is almost always: wider than you think. Tree roots frequently extend well beyond the edge of the canopy, which means the visible dripline is only a starting point — not the boundary of… More
Original post created in 2013 by Ellyn Shea and Leda Marritz, updated in 2026. What do trees really need? Sunlight, water, nutrients, and enough soil for their roots to grow. Pruning is different. Trees evolved for millennia without people cutting their branches, and many trees naturally shed dead or weakened limbs over time. So, strictly… More
Introduction: Supporting Tree Success with the Strongback With Silva Cells, the strongback — our temporary installation lid used during soil placement — is not an afterthought or a mere convenience: It’s an intentional design element that plays a critical role in how soil enters the system, gets compacted, and ultimately performs for trees. This Silva… More
A common assumption in urban tree design is that tree roots do not grow more than 24” below the surface. There’s a reason this idea has stuck around: in many city environments, roots are indeed concentrated close to the surface. Urban soils are often compacted, poorly drained, oxygen-limited, interrupted by utilities, or constrained by pavement… More
Download our research overview document here. Today, the idea that urban trees need real soil volume to reach maturity is no longer controversial — it’s widely accepted among urban foresters and landscape architects. We also recognize that providing that soil volume, especially with systems like Silva Cells, represents a meaningful upfront investment. But decades of… More
Soil structure is one of the greatest influences on pore space in soil, and how easily air, water, and roots can move through a soil. Many people are aware of what soil texture – proportions of sand, silt and clay – they are dealing with on a site; however, few people consider a soil’s structure,… More
Introduction Cities around the world are setting ambitious urban canopy targets, an essential step toward climate resilience and healthier public space. Yet many municipalities struggle to turn those targets into reality. As identified in a recent cross-city urban forest study, the disconnect is rarely a lack of vision — it’s a breakdown in implementation. One… More
The Challenge of Limited Space As cities grow denser and redevelopment accelerates, space is becoming the defining constraint of modern design — and as hardscape surfaces increase, stormwater management becomes more critical. But traditional stormwater infrastructure requires generous footprints (like raingardens) or deep excavation (like large storage tanks): two conditions that are often unavailable in… More
Healthy trees can grow in even the most challenging urban environments, provided they receive enough water, soil, sunlight, and appropriate care. Vigorous urban trees help keep people healthier, cool cities during the summer, reduce energy use, support wildlife, raise property values, and make communities more welcoming. Yet heat and drought in many parts of North… More
It is hard to tell just by looking at a tree-lined street, but soil and its microbes — in combination with trees — can form a powerful system for improving stormwater quality. Some pollutants are filtered or retained by soil, while others are taken up or transformed by plants and microorganisms. The U.S. EPA’s 2023… More
Introduction People often ask us how Silva Cell grows large trees and treats stormwater. The truth is: it doesn’t. At least not by itself. Silva Cell isn’t some magical, mechanical device that generates roots or filters water on its own. Instead, it’s a simple yet powerful framework that lets nature perform at its best, even… More
Susan Day and her team at Virginia Tech published a paper earlier this year about a soil rehabilitation technique called Soil Profile Rebuilding, or SPR. They were looking for a way to rehabilitate soils damaged by land development in a way that would restore their biological function and be more supportive of plant growth. I… More
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