How to Kill Couch Grass

Couch grass is one of the most frustrating weeds in UK gardens. Above ground it looks like ordinary grass, but beneath the surface it spreads through a network of tough, wiry rhizomes that can travel several metres in a single season. Also known as twitch grass, scutch, or wickens, this perennial weed has earned its reputation as one of the hardest to eradicate.

The problem with couch grass isn’t just how fast it spreads. Those white underground stems have sharp tips that can pierce through other plants’ roots, plastic sheeting, and even pond liners. Once it gets into your borders, the rhizomes weave themselves between the roots of your ornamental plants, making removal without damaging your garden almost impossible.

How to Identify Couch Grass

Couch grass (Elymus repens) can be tricky to spot at first because the above-ground growth looks similar to other grasses. The leaves are flat, dull green blades that can reach up to 40cm long. In mid to late summer, yellowish-green flower spikes appear, sometimes reaching 120cm in height.

The real giveaway is underground. While lawn grasses have fibrous root systems that stay in one place, couch grass produces a dense network of pale cream or white rhizomes. These underground stems grow horizontally, spreading outwards from the parent plant in straight lines. Each rhizome has a distinctive sharp growing point that allows it to push through obstacles.

If you suspect you have couch grass, dig up a small section and examine the roots. The white, wiry rhizomes are unmistakable once you know what to look for. They’re tough and springy, quite different from the soft, fibrous roots of lawn grass. Understanding the difference between coarse grass in lawns and invasive couch grass is essential for choosing the right control method.

Why Couch Grass Is So Hard to Kill

Couch grass presents a unique challenge because of how it grows and spreads. The rhizome network is the plant’s survival mechanism, and it’s remarkably resilient.

Every fragment of rhizome left in the soil can regenerate into a new plant. This means that digging often makes the problem worse rather than better. Break the rhizomes into pieces and you’ve just created multiple new plants. Miss even a small section during removal and the couch grass will return.

The rhizomes also grow among and through the root systems of other plants. In borders, they weave between perennials and shrubs, making it virtually impossible to remove them without digging up everything else. Some research suggests couch grass may even release chemicals into the soil that inhibit the growth of surrounding plants, giving it a competitive advantage.

Unlike deep-rooted weeds like horsetail or bindweed, couch grass is relatively shallow-rooted. The rhizomes typically sit in the top 10-15cm of soil. This should make removal easier, but the sheer extent of the horizontal spread and the way it intertwines with other plants more than compensates for its shallow depth.

The Lawn Problem

If couch grass has invaded your lawn, you face a difficult truth. There is no selective weedkiller that will kill couch grass without also killing your lawn grass. Because couch grass is a grass species itself, any herbicide that targets it will harm all the grass around it.

This leaves you with limited options. You can either learn to live with it, keeping it in check through regular mowing, or take the nuclear option: kill the entire affected area and renovate your lawn from scratch.

For lawns where couch grass has become established, the recommended approach is to spray the affected area with a glyphosate-based weedkiller to kill all vegetation. Once everything has died completely, dig over the area to remove dead roots, then re-turf or overseed with fresh grass. It’s drastic, but it’s the only way to get a couch grass-free lawn.

Regular mowing does help prevent couch grass from taking over completely. It stops the weed from flowering and seeding, and keeps the growth in check. However, be aware that the underground rhizomes will continue spreading into adjacent borders, so you’ll need to stay vigilant along lawn edges.

What Actually Kills Couch Grass

When Which? Gardening magazine tested different methods for controlling couch grass, glyphosate spray came out as the clear winner. Most of the couch grass in their trials was killed after just one treatment.

The key to success with glyphosate is timing and persistence. Apply the weedkiller in spring when the couch grass is actively growing and the leaves are producing energy that gets transported down to the rhizomes. This carries the herbicide through the entire root network.

For border infestations, spray every six weeks until all the couch grass has been killed. Protect nearby plants with plastic sheeting or cardboard to prevent spray drift. The strongest weed killer available will give better results than diluted ready-to-use products.

Glyphosate gel is an alternative where spray drift is a concern. It’s slower to work than sprays but allows more targeted application. Paint the gel onto the couch grass leaves, being careful to avoid contact with plants you want to keep.

For severe infestations in borders, the most effective approach is to dig up all your plants, carefully remove any couch grass rhizomes from their rootballs, and temporarily replant them elsewhere. Then spray the infested bed thoroughly and wait until the couch grass is completely dead before replanting.

Manual Removal

If you prefer not to use chemicals, manual removal is possible but requires patience and thoroughness. The good news is that couch grass rhizomes are relatively shallow, typically only 10-15cm deep.

Fork over the soil carefully, working through it systematically to remove every piece of white rhizome. This is painstaking work, but it can be effective if you’re thorough. The problem is that even small fragments will regrow, so you need to sift through the soil carefully.

After initial removal, cover the area with a thick layer of cardboard or black plastic mulch. This deprives any remaining rhizomes of light and will weaken them over time. Leave the covering in place for at least six months, checking periodically for any shoots that manage to find gaps.

For heavy infestations in borders, combining methods often works best. Remove as much as possible by hand, then treat any regrowth with spot applications of glyphosate gel. This minimises chemical use while still dealing with the fragments you inevitably miss.

Preventing Couch Grass

Prevention is always easier than cure. Couch grass often enters gardens as small rhizome fragments hidden in the rootballs of plants brought from elsewhere or in soil and manure.

Before planting anything new, check the rootball carefully for any white, wiry roots that don’t belong to the plant. Remove any suspicious material before planting. If you’re bringing in topsoil or manure from external sources, inspect it for rhizome fragments.

If couch grass is growing on neighbouring land or on the boundary of your plot, consider installing a vertical barrier. Dig a trench about 45cm deep along the boundary and line it with heavy-duty plastic or root barrier membrane. This won’t stop seeds, but it will prevent the rhizomes from spreading through fences into your garden.

Deal with any couch grass as soon as you spot it. A small patch is far easier to eliminate than an established infestation. The same applies to bamboo and other rhizome-spreading weeds like ground elder. Early action saves enormous effort later.

For lawns, regularly cut a fresh edge with an edging iron and turn over the adjacent border soil with a fork. This disrupts any rhizomes that are trying to spread from lawn into borders and allows you to remove them before they become established. A consistent lawn care routine helps maintain strong grass that can better resist weed invasions.

Frequently Asked Questions

Can I kill couch grass without killing my lawn?

No. Couch grass is a grass species, so no selective lawn weedkiller can target it without harming your lawn. The only solution is to kill the entire affected area with glyphosate and then re-turf or re-seed.

How deep do couch grass roots go?

Couch grass is relatively shallow-rooted, typically 10-15cm deep. However, the rhizomes spread horizontally for several metres, making complete removal difficult even though they’re near the surface.

Will digging out couch grass work?

It can work, but you must remove every fragment of the white rhizomes. Even small pieces left in the soil will regrow into new plants. Fork the soil carefully and sift through it thoroughly.

How long does it take to kill couch grass?

With glyphosate spray applied every six weeks during the growing season, most couch grass is killed within 2-3 months. Severe infestations may take a full growing season to eliminate completely.

Can I compost couch grass?

No. Home compost bins don’t reach high enough temperatures to kill the rhizomes, and you risk spreading the weed when you use the compost. Put couch grass in your council green waste bin or take it to a recycling centre.

If couch grass is spreading through your borders and strangling your plants, stop wasting time on methods that don’t work. A professional-strength systemic weedkiller applied at the right time will travel through the entire rhizome network and kill the weed at source. For long-lasting weed control on paths and driveways where couch grass emerges, residual herbicides prevent regrowth for months.