What's a realistic soil volume requirement for street trees?

We'd love to give every tree 1000 cubic feet of soil, but urban spaces often make this impractical. Start with 300-500 cubic feet per tree as a realistic baseline. The exact volume depends on your tree species, local climate, desired mature size, and project goals.
When space allows, always opt for more soil volume. Trees grow faster and live longer with adequate root space. It's like an insurance policy against costly replanting down the road.

 
If soil cells are typically more expensive than alternatives, why should we use them?

The "cheapest" option often costs more in the long run. Mortality rates are high with traditionally planted trees. And the survivors are often stunted or struggle to reach maturity. Being planted this way creates weak, shallow root systems that are much more likely to topple the tree in a storm or break through pavement.
Soil cells cost more upfront, but you're avoiding tree replacements, sidewalk repairs, and ongoing headaches. Trees in properly designed systems grow healthier and live longer. The key is usable soil volume, which is how much uncompacted growing space your system actually provides for roots.

You mentioned 'usable soil volume'. What do you mean by that?

Usable soil volume is the actual space available for root growth, excluding structural components used to support the pavement. Many providers advertise their system's total volume, but anywhere from 15% (post-and-base style soil cells) to 80% (structural soil) may be taken up by structural elements rather than soil.
It's like ordering a large drink that's mostly ice. You're paying for volume you can't use. When comparing methods, focus on actual soil space available for roots, not just the overall dimensions of the underground structure. More usable soil volume means healthier, faster tree growth.

What's the usable soil volume of the RootSpace soil cell? And does it sacrifice strength at all?

RootSpace is 97% usable soil volume, only 3% structure. And actually, the lattice structure of RootSpace makes it the strongest soil cell on the market. Our design distributes loads more efficiently than post-based systems, resulting in superior strength testing results across all measures of performance.

How can landscape architects and designers convey the value to their clients of thinking long term and providing early on for urban trees?

Show them the facts: 25% of traditionally planted urban trees die within months, only half survive long-term. Ask them this: "Would a similar failure rate be accepted for sidewalks or utilities?"

Your client won't remember saving $500 per tree, but they'll remember having to replace dead ones or fix cracked pavement. Frame it as protecting their investment and reputation. Give them workable alternatives, like reducing the number of trees rather than the support system needed for growth. One well-planted tree beats five dead ones every time, and proper infrastructure now prevents costly problems later.

As seen in LASN magazine, July 2025.