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How to Get Rid of Couch Grass Weeds in Your Garden

Couch grass spreads both through underground rhizomes and above-ground stolons, which is what makes it so invasive.

Featured Image: Couch grass / Photo by John Tann / Flickr (cropped) / CC BY 2.0

Couch grass is one of those weeds that seem to invade your garden and keep coming up no matter what you do.

It can be quite challenging to get rid of completely because it’s tough and the underground runners can spread quite rapidly.

How to identify couch grass

Couch grass, or Twitch grass, has a fine leaf blade, is dark green in colour, and is soft to the touch. When you look closely at the leaf blades, you’ll see that they’re quite long and slender. 

You’ll find that the runners that spread across the ground can easily grow up to 20 cm per week. These runners will develop along the main stem at leaf nodes.

The seed heads on couch grass are flattened. The seeds themselves are easily dispersed by the wind and can survive for many years in the soil. 

How does couch grass spread?

Couch grass spreads both through underground rhizomes and above-ground stolons. This is what makes it so invasive and gives it the ability to survive almost anywhere.

Even after digging over a garden bed thoroughly and removing all the couch grass roots, you will probably find that there are a few bits of root or rhizomes that you’ve missed.

These will easily start to grow again and once the grass breaks the surface of the soil, it will quickly spread.

Problems caused by couch grass

Because couch grass is such a rapid and dense grower, it can easily invade your garden beds. Once it’s there, it can be difficult to get rid of. 

Its dense growth habit means that it will compete with your other plants for both water and nutrients in the soil. In fact, if left unchecked, couch grass can easily smother other plants.

According to this article by an urban bushland council in Western Australia, the roots of couch grass also produce a cyanogenic compound that can be toxic to other plants and even animals. When couch grass invades natural bushland areas, it has been found to reduce the growth and germination of native species.

Natural methods for killing couch grass

The best way to control couch grass naturally is to cover it completely so that it doesn’t get any sunlight to grow. You can do this with either a landscape fabric or a thick layer of cardboard or newspaper.

While this method is great for establishing new garden beds because you then cover the fabric or newspaper with thick layers of compost, it’s not ideal for couch grass that has invaded existing beds.

What you do need to be aware of is that it can take some time to get rid of couch grass entirely. This is because it will strive to come back from the underground rhizomes. 

If you only have a small amount in your garden beds, it’s better to dig it out, roots and all, using a good weeding tool. The roots will go down around 20 cm into the soil, so be sure to dig down far enough to get as much of the roots out as possible.

You’ll need to be vigilant and continue to dig out any new grass that comes up as soon as you spot it. It’s also important to not throw any of the couch grass into the compost as it will continue to grow and take over your compost completely. 

If you have a lawn that is primarily couch grass, then it’s a good idea to place a hard barrier between your lawn and your garden beds. This needs to go down at least 20 cm in order to prevent the rhizomes from breaking through.

You also want to ensure that you mow your lawn frequently and always trim the edges well to inhibit the spread of the grass.

RELATED: How to Kill Lawn Weeds

The best herbicide for couch grass

The absolute best herbicide to kill couch grass is a glyphosate-based product such as Roundup. This is a non-selective herbicide so it will kill any other growth that it comes in contact with.

Therefore, you want to apply it carefully with a tool like the Yates Zero Weeding Brush so it only comes into contact with the couch grass. Make sure that you don’t accidentally drop any of the herbicide onto your other plants.

The best time to treat your couch grass problem with glyphosate is in spring as the grass is starting to concentrate on new growth.

Remember to follow up your treatment of the couch grass with further applications of glyphosate until all of the weed has been eliminated.

This could take several applications over several months.

Photo of author

Annette Hird

Annette Hird is a gardening expert with many years of experience in a range of gardening related positions. She has an Associate Diploma of Applied Science in Horticulture and has worked in a variety of production nurseries, primarily as a propagator. She has also been responsible for a large homestead garden that included lawn care, fruit trees, roses and many other ornamental plants. More recently, Annette has concentrated on improving the garden landscape of the homes that she has lived in and focused a lot of energy on growing edible plants as well. She now enjoys sharing her experience and knowledge with others by writing articles about all facets of gardening and growing plants.

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