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The cutting and collection of grass is crucial to creating, enhancing and maintaining wildflower-rich habitats. In this way, the effects of wild grazing are simulated, and nitrogen pollution of soils can be reversed, reducing unnaturally high fertility.
Reduction of fertility means a reduction in growth height, which improves safety for road users. By adopting this method, costs and carbon emissions associated with verge and green space management are reduced and wildflowers can establish and thrive over time.
We believe that grass cuttings should be seen as a resource which could be used to generate revenue and deliver carbon solutions by creating renewable energy and bio-based materials.
The initial purchasing of cut-and-collect machinery (such as a flail collector) can be the biggest barrier to a widespread change in green space and road verge management.
But buying new machinery is an investment that will pay for itself over a viable time frame. Collecting cuttings reduces fertility leading to reduced growth in vegetation. This means that the frequency of cuts can be reduced, delivering the savings that will pay back the initial investment in machinery. Reduced volumes of cuttings will make the collection and disposal operation easier with time.
Dorset Council is a great example of a local authority which has made a success of this kind of economically sustainable transition. Over 7 years the council has reduced its road verge maintenance budget by 45% which has paid back investment in machinery and enabled re-allocation of human resource to more rewarding and value-adding tasks.
Grass cuttings are currently seen as a waste and the perceived feasibility of collection and disposal can be a barrier to the creation of wildflower-rich habitats on road verges and in green spaces.
But removing the grass cuttings can reduce costs and carbon emissions over time while achieving lower soil fertility which restores native wildflowers. See road verge and green space best practice management for more information.
Plantlife is advocating for verges and green spaces to be seen as assets rather than maintenance liabilities and for grass cuttings to be seen as a renewable resource, a novel revenue stream, which can offset carbon and offset vegetation management costs.
See below for case studies and research showing best practice guidance for managing grass cuttings. These aim to embed sustainable practices in green infrastructure and green waste management.
On roadsides, grass cuttings can be deposited into the back verge under trees or into hedgerow bases where it is safe and acceptable to do so. This has the potential to improve road safety because the verge area nearest the carriageway undergoes fertility reduction and therefore a reduction in plant growth height.
A similar approach can be taken in green spaces where cuttings disposal can be at site boundaries or in carefully selected disposal locations.
The vegetation has drawn fertility from the soil as it grew, so by removing cuttings we can displace the fertility from open, grassy spaces (where we want growth height to be lower) into hedgerow bases and woodland edges (where fertility can be converted into woody growth).
On-site disposal is cheaper as there are no biomass transport costs. More grassland biodiversity is encouraged where cuttings are removed and taller growing herbs will provide vegetation structure where cuttings are deposited.
This boosts ecological value by increasing species richness and providing structural diversity whilst reducing costs and carbon emissions.
As part of their standard operations, some local authorities have made it standard practice to cut and collect and to tip small volumes of roadside cuttings along the way into the back verge at hedgerow bases and under trees where safe to do so. This approach has shown that:
A side-discharge mower or following side-delivery power rake can displace the grass cuttings towards the ‘back verge’ as you cut without the need to collect and then tip.
Please note:
Off-site disposal and use of grass cuttings has the greatest opportunity to create a long-term sustainable road verge and green space management system. This could be achieved by recovering value from green waste through composting, anaerobic digestion, and other biotechnologies.
Innovations in cut-and-collect machinery and biotechnologies (such as pyrolysis) have allowed us to start rethinking our green waste management, with the potential of transforming grass cuttings from a waste product into a valuable and sustainable resource. This could be in combination with other organic waste streams which local authorities also need to deal with, such as food waste, woodchip, and kerbside garden waste.
Dorset Council sends its road verge cuttings to a waste-licenced composting service. Cuttings are left to rot down for several months before collection to decrease weight and volume. Although this involves a gate fee, net savings are made by reduced cutting frequency due to fertility reduction and the ability to litter-pick cut material off site, thereby avoiding traffic control for litter-picking operations in a live traffic environment.
Although composting can be part of bio-circular economy by returning fertility and organic matter to land as a bio-fertiliser and soil improver, it releases CO2 and no energy is generated from compost. This means that composting is not seen as the best environmental fate for organic waste within the Waste Hierarchy [1]. By contrast, anaerobic digestion (AD) is a more economic and climate-friendly option that captures heat and methane emissions to generate renewable energy, captures CO2, and recovers nutrients as a bio-fertiliser [1].
Recent research is showing that a process known as pyrolysis could also present a hugely important option in organic waste management, potentially in combination with AD. Pyrolysis produces biochar which has a range of uses including bio-based asphalt, and has the ability to decontaminate pollutants in roadside herbage including the complete breakdown of microplastics.
Trials by Lincolnshire County Council have shown that it is profitable to use grass cuttings as a feedstock in anaerobic digestion.
Research by the University of Leeds has shown that contaminants (such as heavy metals and PAHs) in road-verge grass cuttings are well below levels of concern for use in composting, anaerobic digestion or for spreading digestate to agricultural land as a bio-fertiliser [2].
We identify a ‘sweet spot’ in grass cutting regimes, which promotes optimum plant diversity and harvests biomass for bioenergy most efficiently. The ideal cutting frequency is twice per year, either side of spring and summer spaced by 3-4 months. [3,4]. This standard approach could deliver biodiversity gain without special conservation measures across 90% of our road verge networks (combined with safety cuts) and the majority of our open green spaces where these have not been identified as sites of sensitive ecological value.
Plantlife has worked with South Gloucestershire Council and West Sussex County Council through our contribution to the £3.7 million Greenprint project, funded by the Department for Transport [5,6]. This work has conducted field trials to build the case for grass cuttings to be used to create renewable resources as part of a bio-based circular economy.
Plantlife is also working with a range of stakeholders to encourage changes in biowaste licencing that would enable sustainable use of roadside cuttings and therefore facilitate the cut-and-collect management of road verges. Disposal of grass cuttings from non-roadside green spaces is already covered by standard permitting and this has allowed local authorities to partner with local composting or anaerobic digestion facilities to handle the green waste.
Guidance on Applying the Waste Hierarchy – DEFRA
Plantlife’s road verge and green space work has been generously supported by The Garfield Weston Foundation and MW Tops Wildlife Conservation Project
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