Weak-growing and stunted city trees are not just a sad sight—they represent untapped potential for cities to offer their residents a better quality of life. Cities—whether small towns or mega-cities—are increasingly struggling with the following issues:
- High noise levels
- Excessive CO₂ levels
- Wastewater problems
- Overheating
- High risk during storms
- Unpleasant cityscape
- Poor urban air quality
Healthy and well-developed urban trees can act as the lungs and filters of cities, bringing a whole range of benefits. The Stockholm Tree Planting System—shortly called “SBS”—is therefore an opportunity for city managers AND residents of urban areas.
Looking at the current situation, it’s clear that trees cannot thrive because of surface sealing and being confined in “concrete pots.” The roots are trapped, there’s too little water reaching them, and nutrient supply is severely limited.
The logical result is very weak growth, sickly and vulnerable trees. Most of the surface water is not available to the tree but is instead drained away through sewage systems, which in turn leads to disposal costs for the municipality.
The Solution
All paved surfaces (except for roads) are designed to be open-porous. This allows all surface water to penetrate into the tree substrate and be stored there.
Through a walkable cable duct, all control and maintenance lines are accessible. Each tree receives at least 30 m³ of rootable space. This results in a storage volume of around 5,000 liters of water per tree.
The trees once again show healthy growth and can reach their natural lifespan (over 100 years).
das problem
Trotzdem sind viele Baumpflanzungen Fehlinvestitionen. In konventionellen, verdichteten Baumscheiben sterben Stadtbäume im Schnitt bereits nach 20 bis 30 Jahren – lange bevor sie eine klimawirksame Krone ausbilden können. Und selbst während ihres kurzen Lebens verursachen sie Folgekosten: Wurzeln auf der Suche nach Luft heben Pflaster und Asphalt an.
- Zu wenig Wurzelraum – verdichteter Untergrund unter Asphalt und Pflaster lässt dem Baum kaum Spielraum.
- Zu wenig Wasser & Sauerstoff – versiegelte Flächen leiten den Niederschlag direkt in den Kanal, statt ihn dem Baum verfügbar zu machen.
- Mechanische Schäden an der Oberfläche – Wurzeln, die nach oben drängen, heben Beläge und Bordsteine und ziehen teure Sanierungen nach sich.
How It Works
Surface water from the streets is channeled through shafts into the underlying drainage gravel, where it is distributed and can then evenly infiltrate the tree substrate.
An overflow in the channel ensures that the frost-prone zone remains dry. This keeps all tree roots in the lower substrate and prevents damage from surface deposits.
In winter, a flap system can direct all salt-laden surface water directly into the drainage channel.
The tree pit itself is filled with a structurally rich tree substrate.
Urban Tree Fine Substrate
The pores in the coarse skeleton are filled with the urban tree fine substrate. In the wet installation method (skeleton made of 100/150 mm stones), this fine substrate is flushed into 30 cm thick layers of stones. In the dry installation method, this fine substrate is mixed dry with the stones (40/70 mm) before installation, and the finished mixture is installed all at once.
This fine substrate was developed in cooperation with the City of Graz and DI Erwin Murer and consists of 4 parts washed quartz sand and one part urban tree concentrate. The challenge in development was not only incorporating the right biology and the correct combination of nutrients but also ensuring high stability – after all, the tree is expected to grow in it for several hundred years.
