Trees grow where the soil is moist. This natural process is called hydrotropism: roots actively seek water. However, if watering only occurs on the surface and water does not reach deeper layers, the roots remain shallow and cannot anchor firmly. The same happens when a hard soil layer prevents penetration and roots cannot reach the groundwater. At the Karlsruhe Institute of Technology (KIT), staff in the Biomechanics Department led by Prof. Dr. Claus Mattheck developed a method to guide tree roots into deeper, moister soil layers. A practical example now demonstrates how successful this method can be.
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Parking Lot Planting in 2012
In 2012, the parking lot of a floodplain in North Rhine-Westphalia was redesigned. During this process, 38 Sophora japonica trees were planted. However, important factors were not considered:
- Use of an unknown substrate
- Missing traffic protection
- No thermal trunk protection
This led to severe soil compaction and thermal damage to the trunks. After only a few years, the crowns showed significant damage, such as sparse foliage, premature leaf drop, and a high amount of deadwood.
2023: Revitalization Attempts
To counter this development, revitalization trials were conducted in August 2023. The initiative came from Oliver Heidelberg, an environmental construction and tree expert for the city. He played a key role in implementing the method developed by Mattheck. For 11 trees, so-called gravel cylinders were installed. Four cylinders per tree were placed around the dripline, each with a diameter of 30 cm and a depth of 1 m. To test their effectiveness, the cylinders were filled differently:
- Trees 1–5: Limestone 32/56, Terra Preta soil, mycorrhiza
- Trees 6 and 8: Limestone 32/56, Terra Preta, mycorrhiza, Oscorna Hornamon
- Trees 7, 9, 10, 11: Limestone, Terra Preta, Oscorna Hornamon
Results After Two Years
All trees equipped with gravel cylinders show clear signs of revitalization. Deadwood is no longer present, growth is significant, and premature leaf drop is absent. After two years, the differences compared to untreated trees are clear and noticeable even to non-experts. Treated trees also show richer leaf color. No differences have yet been observed between the different fillings.
Installation of Gravel Cylinders
A gravel cylinder consists of a 20–30 cm wide soil borehole. This is filled with a mixture of coarse gravel and Terra Preta soil. The fertile Terra Preta promotes root growth into the loose gravel column and guides it into deeper soil layers. This allows roots to penetrate hard soil layers. Moisture content in deeper layers is higher than in the topsoil.
Observations show that targeted measures such as gravel cylinders can improve tree vitality in the long term. Prof. Dr. Claus Mattheck is also known for the VTA method (visual tree assessment). You can benefit from his extensive experience and expertise in our seminars. Learn more and register now! https://www.iml-service.com/iml-seminars/