Nature today | Increased biodiversity of green roofs

The team of researchers and students hope to extend the flowering period for sedum vegetation from April to September. For this purpose, a special test site has been set up in Katwijk. The test site contains fields, so-called test green roofs, on which various types of herbs that are attractive to bees were seen. Growth conditions on sedum roofs are especially good for sedum. Therefore, the experimental design for the herbs has varied in offering extra compost and extra water buffer in the form of mineral wool.

Mini Retreats

The spontaneous species that occur in sedum roofs, and which are usually removed again to keep the roof ‘clean’, also have a place in the experimental setup. “We believe that we can increase the habitat for bees, bumble bees and hoverflies with the many different herbs. We create a longer period where there is suitable food available. The green roofs thus form mini-refugees in a stone environment,” explains Hans Krüse. ecologist and visiting researcher at Naturalis, from.

The ultimate goal is to find an optimal condition in which the greatest possible variety of herb species grows. A number of students participate in the research, including Youri Quist, Jennis Groen and Melanie van Grevenbroek. “The city brings a lot of diversity and dynamism with it,” explains Quist, “and dynamism again leads to the development of different habitats. As a result, many insects live in the city, which then have difficulty colonizing themselves. Green roofs can provide the solution; they form green islands where insects can relax and reproduce. “

Mineral wool versus compost

The research project will last at least two years and is now in its initial phase. Biology students Groen and Van Grevenbroek will focus their research on spontaneous plant growth on sedum roofs, under four different conditions: roofs with only substrate, with mineral wool, with compost and with mineral wool and compost. They compare these conditions and see which and how many wild plants are growing. “We expect the compost to grow more,” explains Groen, “but that there will be less species variation. The compost can make one or a few plants dominate, which means that other species do not get a chance to grow. Do not know “what we should expect from the difference between mineral wool and underlay only, so it remains exciting.” Van Grevenbroek adds: “The first plants can already be seen, but it is still too early to draw any conclusions.”

Youri Quist, a student in landscape and environmental management, is also doing her research project at Groene Daken. He focuses on germination and growth of the sown herbs. “I am curious about the effect of mineral wool and compost on the growth of the various herbs,” says Quist. “I want to focus primarily on plant length: how long do different plants grow under different conditions? I expect some plants to do poorly in a nutrient-rich soil and others to do better so the planted herbs can grow out of part.” Using his results, he will write an advisory plan for the further course of the Green Roof research.

Krüse started the research in May 2021 with the construction of a test roof on his garage, where he made the first observations. To tackle the research more thoroughly, a research site was established in the Universal Greenfields area of ​​Katwijk in February 2022 by Dirk Roosendaal of Universal Greenfields with the help of Naturalis and others.

More information

  • For more information on the Green Roofs study, visit
  • For content questions, please contact project manager Hans Krüse, via or 06-34862298. Or stop by the research site: Universal Greenfields, 1st Mientlaan 11, Katwijk.

Text: Naturalis Biodiversity Center
Photos: Atlas Living Environment; Hans Kruse, Naturalist

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