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Expert Advice on Getting Rid of Couch Grass


Couch grass (Latin name Elymus repens) is a quick growing, invasive type of grass which appears to contribute nothing to the overall appearance or productivity of a garden or allotment. Another commonly used name for this weed is Twitch Grass. It is a pain in the neck in your garden and mine, nothing more, nothing less.

This article explains several methods, organic and chemical, for removing and eradicating couch grass. Use the navigation box below to skip to the section most important to you if you don't have time to read the entire article.



HOW DOES COUCH GRASS GROW


Some background information about how couch grass grows and the conditions it prefers is always useful in fighting such a powerful weed. 

Although couch grass is considered a weed by UK gardeners and allotment holders it does actually have a use in some circumstances! Firstly, in some parts of the world couch grass is encouraged because it is a primary source of food for cattle and other animals. Its second most common use is to bind soil together to prevent erosion by wind and water.

Couch grass arrives in your garden or allotment initially by two means. By far the most common is through small root parts in the soil of plants which are transferred to your garden.

The second is by means of seeds. Insignificant flowers are produced in July / August time and these form seeds which can be spread by wind, water and carried on wildlife such as birds. Once it arrives in your garden however, forget about it spreading via seeds, it is the roots which enable it to colonise large areas quickly.

 Seeds of couch grass
Couch grass seeds

When a root establishes, it send up grass stems, typically every 5 to 10cm along the root. The grass stems absorb energy from the sun which allow the roots to grow further. The roots store unusually large amounts of energy and they can continue to grow and survive for long periods of time without energy from the sun. Eventually they will die if they do not receive sunshine.

PROBLEMS CAUSED BY COUCH GRASS


Because of its ability to begin growth early in the season couch grass can smother other plants before temperatures are high enough to establish themselves at the beginning of the season. This weed also absorbs large amounts of nutrients from the soil making it difficult for other plants to grow well. 

Couch grass roots also secrete acids and other phytotoxins (poisons for other plants) which reduce the ability of surrounding plants to absorb nutrients from the soil. This has a direct impact for gardeners not only when the grass is growing but also when it is killed (rather than removed) by herbicides or excluding light. The reason for this is that, as the roots of Couch Grass decompose, they still secrete phytotoxins which can damage new plants.

Very little conclusive research has been conducted on how long these phytotoxins remain in the soil after couch grass has been killed. Our investigations suggest that the ground is partially "poisonous" to new plants for a month or so after couch grass is killed. The best research we could find was this document here.

The solutions we propose below to eradicating couch grass are based on three situations:

  1. Where this weed has established itself amongst other cultivated plants, this is the typical situation in a UK garden.
     
  2. Where the weed has established itself on a patch of land that is uncultivated. This is a typical situation for a new allotment or patch of land that has not been cultivated for some time.
     
  3. Where couch grass has taken hold of an existing lawn area.

Whichever of the methods you use below make sure that you dig a trench around the treated area about about 45cm wide and 15cm deep. This will allow you to see any roots crossing from the untreated area to the treated are and easily remove them.

KILLING COUCH GRASS WITH HERBICIDES


Herbicides are garden chemicals designed to kill plants, such as Couch Grass, which produce green growth above ground. The most effective herbicides (by a very large measure) available to amateur gardeners in the UK for killing grass have the key chemical ingredient glyphosate. This chemical is extremely efficient for killing grasses but it also has some potential disadvantages which are:
  • A significant proportion of people believe or suspect that glyphosate damages the environment, wildlife and humans. This a factual article so we won't discuss this subject here, just be aware that concerns do exist. To investigate further simply type in something like "glyphosate poison" into your favourite search engine and research away.

    For those who want a starting point for research on this subject try this article here. It has lots of links in the text to help you widen the research area.

    If you do this research, weigh it up with the implications of not using a chemical such as glyphosate. There are implications and you need to be aware of them as well as the possible problems.
     
  • It damages or kills almost all plants it touches where they have green leafy growth. This is not a selective herbicide, it kills or damages plant life indiscriminately.
     
  • Aside from small areas, the preferred method of applying this herbicide is by spraying. Even the slightest amount of wind can cause the spray to drift several metres causing damage to nearby plant life where none is intended.

If this method of killing glyphosate is to be used on large areas we suggest that it is most effective when the following method is used:

  • If the area contains weeds taller than 5cm / 2in, use a strimmer to clear the area of most of the top growth. Rake away the strimmed top growth to fully expose the weeds to sunlight. This task is best done in April time for effective control of Couch Grass. It will stimulate the grass into maximum growth mode.
     
  • Wait for two weeks to let the grass form new growth. Then spray with the herbicide following the instructions on the packet or bottle. This includes only spraying when the ground is relatively dry and no rain is forecast for 24 hours or more.
     
  • Leave the area alone for three weeks for the effects to be seen. If some weeds are still present undamaged, re-spray those surviving

KILLING COUCH GRASS BY SMOTHERING IT


Where medium to large areas of ground, such as an allotment or the end of a garden, are over-run with couch grass and other weeds this method works well with minimum effort although it will take a season to completely clear ground.

It is often used in conjunction with the "dig it out" method in the next section. One patch of weeds is smothered and another area, required in a shorter time, is dug.

Weed Control fabric

Smothering couch grass and other weeds works on the basis that if all light is prevented from reaching them, they will die. For best results, cover the weeds for nine months to a year. Lots of material can be used to cover the weeds, the most common are listed below:

  1. Weed suppressing fabric bought online (the cheapest source) or at your local garden centre / diy store. It is typically sold in two weights, 50g and 100g. The heavier the material, the more durable it is. However for most uses, 50g weight is more than adequate.

    A proven weed suppressant fabric is sold online by Harrod Horticultural and can be found here. It has the advantage that it can be re-used with confidence for several years. Doing this allows you to clear part of an area one year, then re-use the fabric to clear a further area the next year.

    If the weeds are much taller than 5cm / 2in high, strim them first to allow the fabric to sit evenly on the surface. Rake away the strimmed weeds and then lay the fabric on the top. The fabric will need to held in place to stop it blowing away. Stones or loose earth are ideal for this purpose.

  2. Black plastic is a cheaper alternative to purpose-made weed fabric but it has disadvantages. Black plastic (for instance large black bin bags) also exclude light but weeds can, and often do, break open the plastic and grow through. They also blow away easily when the surface is broken.
     
  3. Carpets are sometimes used to exclude light but be sure not to used foam backed carpets. The foam will break up after a month or so leaving a non-biodegradable mess. Many allotment societies forbid their use. You will also need to store or dispose of them after use and carpets do not store easily or neatly in small areas.

When the weed suppressant has killed the weeds it can be stored away for later use and the ground can be dug and cultivated as normal.

DIGGING OUT COUCH GRASS


This is the most labour intensive way to clear a medium to large sized area of couch grass and / or other weeds. It involves digging the area to a depth of about 15cm to 20cm (6in to 8in) deep with a fork. As you dig, break up the soil and the roots of couch grass (and most other weeds) can be removed. 

This won't get rid of 100% of the weeds because some will inevitably be overlooked but if you keep an eye out for re-appearing weeds over the next month or so then they can easily be pulled out, mostly intact, from the freshly dug ground.

The downside is of course the effort involved but you need to consider that, whatever method you use, the ground will still need to be dug at some stage before planting crops or ornamental flowers. The extra effort of removing the couch grass roots during digging is, in our opinion vastly over-stated. You will also end up with soil of an excellent texture.

AMONGST OTHER PLANTS


Probably the most difficult situation with Couch Grass is where it has invaded an area already containing ornamental plants or vegetables. Clearly, in this situation spraying with chemicals is not an option because, however careful you are, overspray will also kill existing plants.

Our suggested method is to first carefully cut away any grass foliage above ground. Then use a trowel to gently dig around the plants and remove as many grass roots as you can without damaging the roots of existing plants.

Finally and most importantly, then use weed-suppressant fabric or black plastic to cover the area. Cut holes or slits in the fabric to allow it to go around the stems of plants as near as possible. The weed-suppressant fabric can be left in place in place indefinitely because it is designed to allow rainfall to pass through to the soil below. Hold it in place (and disguise it) with a thin layer of soil.

If you use black plastic to cover the ground around plants be sure to pierce it in lots of places to allow moisture to sink into the ground below. This will inevitably allow grass stems to re-appear but they must then be removed by hand.

FACTS ABOUT COUCH GRASS


Below is a list of facts of facts about couch grass which are probably useless, but who knows, they may may open up a weak point in the growth cycle of this weed to you that others have not spotted.
  • Elymus repens is a perennial plant with a lifespan that is limited only by surrounding conditions
     
  • The roots are normally shallow but can go down as far as 20cm / 8in.
     
  • The roots can run underground as far as 60cm / 2ft before sending up a shoot. Much further than 60cm from an existing shoot and they tend to give up and concentrate growth in a different direction.
     
  • Elymus repens is native to Europe and Western / central Asia. It has spread to almost all parts of the world where cultivated plants exist.
     
  • It can grow in almost conditions, wet, dry, alkaline and acid soils, salty areas included. It fails only in full shade.
     
  • Growth of the plant occurs within the range 2°C to 35°C (36°F to 95°F). New shoots above or near ground level can be killed by frost.
     
  • The ideal temperatures for rapid growth are 19°C to 25°C (67°F to 78°F) although don't underestimate its ability to grow 10 degrees either way of this range.
     
  • Spring growth begins earlier for Couch Grass compared to most other grasses, vegetables and ornamental plants.
     
  • Where land is permanently grazed by animals such as sheep, cows etc., couch grass fails to establish.
     
  • Flowers and seeds are produced from mid June to mid August depending on local weather conditions in the UK.
     
  • When established, the plant spreads principally through roots (called rhizomes) rapidly growing sideways. Seeds are a secondary method of the plant spreading itself.
     
  •  Elymus repens is self-sterile which means each plant requires another couch grass plant to produce flowers (and therefore seeds). This is one reason for the minimal production of seeds.
     
  • Seeds can remain dormant in the soil for three years.
     

COMMENTS / QUESTIONS LEFT BY OUR READERS

Date: 28 May 2016 From: Susan
The problem I find when trying to dig couch grass out of my allotment is that it is impossible to not take a significant amount of soil out at the same time as the grass and then how do you dispose of it?

ANSWER: You have two real options. Firstly you can try and separate as much soil as possible from each clod as dig. If the soil is clay this can be difficult because the roots of couch grass will bring the soil together. I find that leaving it to dry, upturned, for a dry day does help significantly.

The second method is dig up each clod and place it, upside down in a heap. This will kill some of the couch grass over a moth or two but is not something I would recommend.

I have seen some dig up the clods and simply throw them away. This is the easiest method but you will effectively be removing the most fertile top soil.

We have temporarily disabled more questions because we are unable to cope with the workload of answering them at the moment. We are seeking more staff to help with this problem.