The lawn as living space: mowing methods and biodiversity

A study by the University of Hohenheim shows that under certain conditions, robotic lawnmowers can support more biodiversity than ordinary manual mowers.

Red poppies, cornflowers and other wild flowers; in the background, a STIHL iMOW® robotic mower with charging station in a garden

Overview: study results

  • A study conducted by the University of Hohenheim in cooperation with STIHL has concluded that, under certain conditions, robotic mowers such as the STIHL iMOW® support more biodiversity than conventional manual mowers with grass collection boxes

  • At a cutting height of six centimetres, plants tend to adapt and grow out rather than up

  • Increasing biodiversity in your home garden means it is necessary to tolerate flowering plants, as lawns are generally not biodiverse areas

  • If you do not want flowering plants on the lawn, you could instead plant flower borders along the edges

Mowing grass and biodiversity

Sustainability and species protection are becoming increasingly important even in our home gardens. Whether by creating wildlife-friendly gardens or using environmentally friendly power tools, more and more people want to play their part when it comes to nature conservation. Robotic lawn mowers are frequently viewed with scepticism in this context, with autonomous robotic mowers such as the STIHL iMOW® repeatedly facing accusations that their mowing methods do not provide for biodiversity.

Sustainability is important to us at STIHL. That’s why we supported Master’s student Maximilian Lang from the University of Hohenheim in researching his thesis titled “Investigations on the influence of robotic mowers on the lawn habitat”. The astonishing result: robotic mowers suchas the STIHL iMOW® do not restrict biodiversity more than regular lawn mowers, but can actually allow for more plant diversity under certain circumstances.

We have summarised the most important conclusions of the study for you below. If you are interested, you can download a detailed technical article from our press office at the bottom of the page ↓.

A detailed look at the test setup

With technical support from development engineer Jörg Elfner, Lang’s thesis investigated the impact on lawn biodiversity of two mowing methods: mowing and collecting the cuttings with a manual mower and collection box, and mulching via self-driving robotic mowers. STIHL supported the study by providing a test area and the necessary mowers.

Overhead view of a green space on the factory grounds divided into four, with STIHL robotic mowers and a manual lawn mower

The student used a 300-square-metre plot of land on the STIHL factory premises in Waiblingen and divided it into four sections. To investigate the growth and flowering behaviour of plants based on the mowing method, five typical lawn plants were planted in an even distribution across all sections:

  • Daisy (Bellis perennis)
  • Ribwort plantain (Plantago lanceolata)

  • Common dandelion(Taraxacum officinale)

  • White clover (Trifolium repens)

  • Creeping speedwell (Veronica filiformis)

During the test period between May and September 2020, two sections were mown with a STIHL RMA 339 C cordless lawn mower and two with a STIHL iMOW® RMI 422 robotic mower. For both methods, the cutting height was six centimetres on one area and three centimetres on the other. 

The robotic mower was used every day on its sections, while the other two areas were cut every two weeks with the manual lawn mower. Within the area mown to a height of six centimetres every day by the RMI 422 robotic mower, sub-areas were also sown with RSM 2.2, RSM 2.3. and RSM 2.4 grass seed mixes, and growth and flowering behaviour were specially monitored.

The impact on fauna present was investigated by means of insect monitoring on all sections, using a randomly placed measuring quadrant to ascertain visits by hymenoptera such as bees and bumblebees, which are of great importance for plant pollination.

Close-up of a bee on a pink flower with a STIHL iMOW® robotic mower in the background

Flowering plants tolerate robotic mowers

The evaluation of the investigation results revealed some interesting findings: the flowering plants on the robot-mown lawns showed a similar cutting tolerance to their counterparts on the hand-mown lawns, and even had a much larger coverage ratio in the case of some plant types. One particularly exciting finding was that the plants tended to adapt to the mowing method and grow outward rather than up.

There was less flowering on the hand-mown grass however, which can be explained by how a conventional lawnmower operates: the airflow generated by the highlift blades pulls the plants upwards and cuts off flower heads. A robotic mower, on the other hand, does not generate this air movement.

Overall results varied widely depending on plant type, mowing system and cutting height, but on the sections of grass that were mown daily with the robotic mower,constant flowering was observed throughout the entire test period, while flowering on the hand-mown sections was highly variable. 

Furthermore, in terms of turf density, consistent coverage of 100% was observed on the robot-mown areas, while coverage fell continuously to 80% on the hand-mown sections.

Close-up of bright blue cornflowers in front of some other wildflowers

Raising awareness of biodiversity in green spaces

How can these study findings be interpreted with respect to the use of robotic mowers? First of all, it is important to be aware that conventional lawns are not generally considered biodiverse green areas.

That said, the variety of species on a lawn can be increased by using seed mixes that include a certain proportion of flowering plant seeds. Lang was also able to prove this in his study by sowing different lawn mixtures. 

If you opt for this approach, the daily use of a robotic mower at the maximum cutting height can lead to spreading growth and an increased abundance of flowers,depending on the species.

But not everyone wants flowering plants on their lawn. Do you prefer an even, green carpet, but don't want to forgo a wildlife-friendly garden? 

STIHL iMOW® RMI 422 PC robotic mower on a green lawn next to a flowerbed bordered with flat stones

The evaluation of the insect monitoring demonstrates that edging with blooming strips featuring tall plants that flower for long periods is particularly useful for encouraging biodiversity, because it gives insects, spiders and other small animals access to sufficient food and supports reproduction.

In this case too, you can benefit from the smart technology of the STIHL iMOW® robotic mower. When installing your robotic lawn mower, simply place a boundary wire around your beds. This helps the robotic lawn mower to recognise the area to be mown – so it will reliably maintain and cut your lawn edge.

“This means garden designers and owners as well as planners and managers of public green spaces have almost unlimited scope in the design and maintenance of their properties,” says development engineer Jörg Elfner. 

Because it is not just the mowing method that leads the way in increasing biodiversity in your garden, but predominantly the garden planning and design. So with the support of research such as this by Maximilian Lang, at STIHL we also want to help raise awareness of the fact that it is possible to increase biodiversity even in our home gardens. Together, we can make people and animals feel at home there in equal measure.  

Download: The lawn as living space

If you are interested in finding out even more about the background of this study, the test setup and a detailed analysis of the results, you can download the full technical article from our press office as a PDF: