---
title: "Tree Pit / Tree Trench"
url: "https://commonwaysystem.org/patterns/elements/tree-pit-tree-trench/"
id: "ELM-TPT-29"
description: "The below-grade excavated and engineered soil volume, either an individual pit or a shared linear trench connecting multiple planting locations, providing root space and often structural soil to support street tree growth beneath a sidewalk or paved surface."
updated: "2026-09-26"
---

# Tree Pit / Tree Trench

`ELM-TPT-29`

Recommended Element

Tree Pit / Tree Trench

The below-grade excavated and engineered soil volume, either an individual pit or a shared linear trench connecting multiple planting locations, providing root space and often structural soil to support street tree growth beneath a sidewalk or paved surface.

## Why this pattern exists

A tree’s long-term health depends far more on below-grade soil volume and quality than on what is visible at the surface; a standard small pit surrounded by compacted pavement subgrade starves a tree’s root system, while a shared trench connecting multiple pits dramatically increases available soil volume. This pattern exists to document that structural, below-grade design distinct from the visible tree itself.

## Key considerations

-   Shared trench designs generally outperform isolated individual pits for tree health and should be preferred where feasible[1]
-   Structural soil or suspended pavement systems may be needed where a trench must also support pavement loads above it
-   Coordination with underground utilities is essential early in design, since a trench’s extent can conflict with existing utility corridors

## Related patterns

[Street Tree](https://commonwaysystem.org/patterns/elements/street-tree.md) (ELM-STT-28) (the visible element this pattern supports); [Pervious Strip](https://commonwaysystem.org/patterns/elements/pervious-strip.md) (ELM-PVS-21), [Bioswale](https://commonwaysystem.org/patterns/elements/bioswale.md) (ELM-BIO-19) (related below-grade stormwater and soil treatments)

## References

1.  Evidence-based [Lindsey, J.P. and Bassuk, N. (1991), "Specifying Soil Volumes to Meet the Water Needs of Mature Urban Street Trees and Trees in Containers," _Journal of Arboriculture_ 17(6). Direct evidentiary basis for shared trenches, pooling soil volume across pits, outperforming isolated small pits.](https://auf.isa-arbor.com/content/17/6/141)