Scientific field research into tree granulates starting

28 february 2019

A five year long scientific field research into tree granulates starts in Amsterdam, commissioned by the Amsterdam municipality. Eight companies, seven of which with RAG certified tree substrates, participate. The research will answer the question of how the growth development of trees is in tree granulates compared to traditional growing media.

There is less and less growing space available for tree roots underneath roads, streets, bicycle lanes and parking spaces in municipalities. This growth is also put under pressure following the traffic overload. Tree granulates are specifically intended for application underneath hard roads.

Independent research

environment and cooperates with tree experts. In the meantime the preparations for the field research have begun along the Abidjanweg in the Western Harbour Area “Westelijk Havengebied”. The eight companies have delivered their tree granulates and this month the planting of 180 elm trees (Ulmus Rebona) has begun.

The test area is along the Abidjanweg in Amsterdam.

The testing set up

The trees are tested in 15 different tree granulates. Every separate plant compartment of 2 x 2 x 0,8 meter containing the substrate is repeated 12 times, spread out on the plot. These repetitions are necessary for a reliable result, because several other factors can also influence the growth of the tree. The tree granulates are covered with a hard surface of concrete clinker bricks. One growing space per substrate will remain open as a reference. The development of the trees will be studied over the course of five years. Mainly the growth development above the ground is looked at.

Valuable insights

In order to obtain the RAG quality mark, several physical properties of tree granulates are already looked at, including bearing capacity, measured with the ‘RAG Landscaping m3 box’. The growth results of the research in Amsterdam lead to valuable insights for RHP. Insights in order to further develop the knowledge built with the norms for RAG certified tree substrates. For the participating substrate producers the research results can serve as a foundation for the development of a new generation of tree substrates with yet a higher quality.

RAG tree granulates tree substrate quality mark


The companies that have supplied RAG certified tree granulates for the research are: AH Vrij Groen, Grond en Infra, Den Ouden, Gebr. Olieman, Heicom, JdB groep, Tree Ground Solutions and Van Doorn - Soest. BVB Substrates also has supplied tree granulates for the experiment. Rob Scholman, technical advisor at RHP, is part of the research group in which for example Wageningen University and several tree and soil experts also take part. The role of the research group is setting up the research plan and leading the field research, which will be finished in 2023.

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