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The cutting and collection of grass is crucial to creating, enhancing and maintaining wildflower-rich habitats. 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 seem to 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 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 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 waste management.
By collecting and disposing of the grass cuttings on-site, through methods such as side-discharge or using carefully chosen sacrificial (rot-down/disposal) sites. we can displace the fertility from open, grassy spaces (where we want fertility to be lower) into hedgerow bases and woodland edges (where fertility can be converted into woody growth). On-site disposal can encourage species-richer grassland with zones of more structural diversity whilst reducing costs and carbon emissions.
As part of their standard operations, some local authorities have set about identifying sacrificial sites along their road verge network to dispose of grass cuttings. This approach has shown that:
A side-discharge mower displaces the grass cuttings to the ‘back verge’ as you cut. Soil conditions for wildflowers are enhanced across most of the verge by displacing the fertility to the hedgerow or the ‘back verge’. Taller herbs in the back verge and hedgerow shrubs and trees will build structural and seasonal diversity which complements the verge biodiversity.
This method should not be used on sites where the back verge, hedgerow, or woodland edge is populated with protected species.
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 hydrothermal carbonisation) 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 in reduced cutting frequency from 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 . By contrast, anaerobic digestion (AD) is a more economic option that captures heat and methane emissions to generate renewable energy, captures CO2, and recovers nutrients as a bio-fertiliser .
Recent research is showing that a process known as hydrothermal carbonisation (HTC) could also present a hugely important option in organic waste management, potentially in combination with AD. HTC produces hydrochar which has a range of uses including bio-based asphalt, and has the ability to decontaminate potential roadside contaminants.
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 . Canterbury Christ Church University is currently investigating micro-plastic content.
We identify a ‘sweet spot’ in grass cutting regimes, which promotes both optimum plant diversity and harvests biomass for bioenergy most efficiently. The ideal cutting frequency is twice per year, spaced by about 3-4 months either side of mid-summer and can be applied to 90% of grassland green spaces and road verges outside designated nature reserves [3,4].
Plantlife is currently working with South Gloucestershire Council and West Sussex County Council through our contribution to the £3.9 million Greenprint project, funded by the Department for Transport [5,6]. This work will conduct 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 inform green waste management licencing to facilitate the off-site removal of grass cuttings from road verges. The waste management licences, concerning grass cuttings from non-roadside green spaces, already enable off-site removal and has allowed local authorities to partner with local composting or anaerobic digestion plants to handle the green waste.
Guidance on Applying the Waste Hierarchy – DEFRA
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