‘Stockholm Tree Pit’ Saves Dying Urban Trees

A method for planting trees in concrete-laden urban spaces is taking root — excuse the pun — across Europe, reports Peter Yeung for Reasons to be Cheerful. The “Stockholm tree pit” is an innovation created in Stockholm, Sweden as a response to an assessment of the city’s trees that found two-thirds of the city’s trees were dead or dying.

“The design involves digging a pit and constructing a frame underground around the tree’s roots, and then filling said pit with a mixture of soil and stone, sometimes including biochar, to both aerate and fertilize the soil.” The permeable layers allow the tree to receive stormwater and air than they would in traditional soil surrounded by paved spaces.

“Proponents say the method has a number of benefits, including the fact that pits can be installed around existing trees, they can bear the weight of heavy-vehicle traffic, they require little topsoil — a resource that is becoming scarce — and they need less watering than traditionally-planted trees.” Trees that use the pits are growing to larger sizes and absorb and filter more rainwater. “The municipality estimates that 2.3 million liters of rainwater are managed by the trees per year, and consequently, 4,600 square meters of roofs and sidewalks have been disconnected from the sewage system, reducing the burden on water treatment services.”