Back to blog listings

The power of purple moor grass

Posted: Wednesday 17th May 2017 by DevonWildlifeTrust

Purple moor grassPurple moor grass could play an important natural role in flood defences

We've been experimenting in growing a particular kind of grass which could play a role as a natural flood defence mechanism. Simon Tomasso from our Upstream Thinking project explains...

Culm grasslands and in particular pastures dominated by purple moor-grass can store five times more water than intensively managed land. Not only does the water get stored in this grassland, the way in which the water is then slowly released is of equal importance. Acting as a natural farmed flood defence mechanism, Culm grassland could play an important part in a future where more extreme rainfall and drought events are predicted.

Grass with potential

These grasslands also have great potential in reducing water treatment costs. Devon Wildlife Trust’s approach has been recognised and supported by South West Water as part of its wider Upstream Thinking initiative (working in conjunction with Westcountry Rivers Trust, Exmoor National Park and Cornwall Wildlife Trust). This estimates that every £1 invested in landscape scale approaches to water management can yield up to £65 of saving per customer over a 30 year period.

Our purple moor grass growing trial site in North Devon

Research from the University of Exeter has shown that if Culm grassland were to be restored to its geographical range of 1900 it would produce a landscape capable of storing 750% more water and carbon than its present capacities.

With facts such as those listed above, it’s plain to see why we are still trying to create species rich purple moor-grass dominated pastures

Over the years Devon Wildlife Trust has carried out lots of interesting methods of Culm creation, and although results have been good, the key species on our Culm grasslands for water storage which is purple moor-grass, has been lacking. Being a deciduous grass, it’s the annual shedding of its dead vegetation that creates the humic layer of partially decomposed matter that is vital for water storage and carbon retention.

Seeds of success

Although purple moor-grass has been spread onto numerous restoration plots it seems to have had limited success in its establishment within the sward so far, on sites where it already existed it has come back in good quantities. This has lead us to look at a germination test to see if it will germinate using methods that can be easily replicated with our agricultural machinery on a landscape scale.

We began by ploughing a piece of organic semi improved pasture, typical of ground we have access to when carrying out Culm creation with private landowners. This plot was then worked using spring tines to create a rough tilth. 11kg of purple moor-grass rich seed was brush harvested from a DWT nature reserve and spread over the plot in the autumn of 2015 shortly after harvesting.

We have looked at 4 methods of germination in the autumn and replicated it in the spring, leading to 8 trial plots.

Plot Autumn 

1 Seed shallow raked into prepared soil 

2 Seed raked into prepared soil and covered with agricultural fleece 

3 Seed broadcast onto the prepared soil surface 

4 Seed broadcast onto the prepared soils surface and covered with agricultural fleece 

Plot Spring

5 Seed shallow raked into prepared soil

6 Seed raked into prepared soil and covered with agricultural fleece

7 Seed broadcast onto the prepared soil surface

8 Seed broadcast onto the prepared soils surface and covered with agricultural fleece


How have things faired?

Well, one thing that we do know is that it will germinate!

Another thing we have learnt is that although initially the fleeced plots showed the highest germination rate, they also gave other aggressive plants such as creeping buttercup too much of a head start and they have smothered a lot of the Purple moor-grass. At the start of the first growing season in 2016 it looked very much as if Plot 2 and Plot 4 were the best but at the end of the season the plot with the most established young plants was Plot 1.

Simon checks the number of species in a newly grown area

Winter in 2016 saw us cut and remove the vegetation on half the plot leaving the other half as an unmanaged control. So far this season it looks as if Plot 1 and 2 are the front runners in terms of Purple moor-grass and plenty of other desirable culm species are also showing very well, such as Devil’s-bit scabious, Betony, Square stalked St John’s Wort, Bedstraw, and in particular Sneezewort has shown in abundance. The cutting and removal of vegetation certainly seems to favour the newly emerging plants, with a lot of the species already being lost amongst the uncut areas. At the moment the spring sown seeds have fallen behind the autumn sown on all methods, but it is an ongoing trial so only time will tell.

The future

Hopefully this trial, along with other work funded by the Environment Agency through our Culm Grassland Natural Flood Management Project will bring us ever closer to creating something that not only benefits wildlife, but will act as a natural farmed flood defence mechanism. In the current economic climate, where habitats and wildlife can fall down the agenda this can only be a good thing.

So raise a glass……..(of clean, slow released tap water)……to purple moor Grass.

Find out more on Upstream Thinking and its work


Read DevonWildlifeTrust's latest blog entries.


There are currently no comments, why not be the first.

    Post a comment