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Green roof vegetation mats: all you need to know…

by Matt Downs

Pre-grown vegetation mats, whether they be wildflowers or sedum species, are a quick and convenient way of achieving plant coverage on a green roof. But what are they and how are they produced? We’ve talked to two GRO members who are experts in the field of growing vegetation mats to find out more about what they do.

Harrowden Turf is a national grower with nationwide depots as well as arable and turf farms in East Anglia and Lancashire, where alongside growing food crops they produce turf, sedum matting, seed and wildflower products.

Wildflower Turf has production units in Hampshire and in Yorkshire and are a leading innovator and advocate for landscaping and green roof products that encourage biodiversity net gain. This company is actively involved with green roof training and offers regular courses in association with the Living Roofs Academy. 

What do vegetation mats consist of?
In general, a vegetation mat has just two components; growing medium and plants. The mat is held together by a densely interwoven net of living roots. In some products there may be a carrier fleece to help with handling and transportation.

The plant species mix tends to be a one-size-fits-all solution, unless of course the mats have been bespoke grown for a particular project.

Above: Enviromat Sedum Matting production at Harrowden Turf in Norfolk.

The growing process
The growing process for vegetation mats starts long before any seeds are sown. Behind these deceptively simple products are years of intense research and development into substrates, seed mixes, growing techniques and handling properties.

Take growing medium for example. Not only does it need to support the chosen mix of plant species, but it must also be suitable for use on a green roof. Natural topsoil is out of the question which means that our growers need to source substrates that meet the criteria of The GRO Code Of Best Practice.

A wonderfully biodiverse green roof sward created using vegetation mats supplied by Wildflower Turf.

Seed mix matters
Seed mixes need careful consideration from the grower. Both vegetation mat growers we talked to have the benefit of years of experience behind them. Couple that with extensive, continuous research and development and you can be confident that their seed mixes are suitable for most green roof projects where there is a reasonable depth of substrate.

Reading the market
Vegetation mats do not appear overnight. It can take months of careful nurturing to bring sedum matting or wildflower matting into a saleable condition. Our growers have to anticipate sales levels at least 12-18 months in advance if they are to satisfy all of their potential customers.

In addition to market forces, our growers are, of course, at the mercy of the weather. Vegetation mats are grown out of doors so that the plants are acclimatised to all conditions. This can have a dramatic effect on growth rates.

In conclusion
When you are designing and specifying your living roof, spare a thought for the people who are growing the vegetation mats that will bring life to your project. Learn as much as you can about their processes and the information they need in order to help you. If you anticipate placing an extra large order, let them know as soon as possible so that they can be sure to grow enough matting to cover your needs. Ditto for if you have a specific seed mix that needs to be custom grown. Talk to your preferred supplier about the best way to handle, install and nurture their products and, if you can, attend training courses where you can gain hands-on experience of handling the products.

In short – form a partnership with your grower, just as you would with the suppliers of your waterproofing and other green roof components.

harrowdenturf.co.uk / wildflowerturf.co.uk

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