Couch grass (Elymus repens) has one of the worst reputations in the gardening world. It spreads via deep horizontal rhizomes that regrow from even the tiniest fragment — which is why farmers and gardeners have been fighting it for centuries. In temperate climates across the world, it is classified as one of the most tenacious agricultural weeds.
On a coastal dune, however, the story is entirely different. Here, couch grass plays a vital role in the earliest stages of dune formation — binding loose sand with its dense root network, tolerating salt spray, drought, and the nutrient-poor soils that defeat almost everything else. Without it, the dune simply blows away.
Ragwort (Jacobaea vulgaris) faces a similar paradox. Legally classified as an injurious weed under the Weeds Act 1959 — and genuinely toxic to horses and cattle — it is one of the most contested plants in Britain. Yet it supports over 77 invertebrate species, 30 of which depend on it entirely to complete their life cycle. The cinnabar moth (Tyria jacobaeae), with its unmistakable yellow-and-black caterpillars, is its most famous resident. On coastal dunes, away from livestock, conservationists actively protect it.
Sand dunes are among the most threatened habitats in Wales — over 80% have been lost or degraded in the last century. The greatest threat isn’t erosion: it’s the opposite. When dunes stop moving, coarser vegetation takes over and the open sandy microhabitats that hundreds of species depend on simply disappear. Natural Resources Wales actively scrapes back vegetation on managed dune systems to keep the sand moving — and the habitat alive. Dunes also act as natural flood defences, buffering storm surges along the entire coastline.
What one place calls a weed, another calls a guardian.