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How to get rid of Couch Grass with clay and no dig beds?

#1 · 5th May 2024, 1:33 pm

Hello all,

I have a double whammy issue in my teeny new garden. I knew the soil was somewhat clay - not too heavy, some sand, but definitely clay - and had worked out my plan for that. But I went out this morning and saw the dreaded shoots of couch grass which I recognised from my allotment! Nooo! So, I had been planning mainly no-dig and had saved my moving boxes for a cardboard and compost mulch, but is that out of the window now? Should I get on with digging out the couch grass? But should you dig clay? What a dilemma! Any suggestions appreciated. I’m aiming for a very informal garden - trees, roses, perennials, and ground cover to replace the lawn. A corner was reserved for raised veg beds but I don’t want it all to be given over to raised beds. I’m an experienced gardener and can dig and fork out the roots if that’s the best solution. Thank you ☺️

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#2 · 9th May 2024, 10:14 am

Quote from Lee Garden Ninja on 9th May 2024, 10:14 am
Hi @cbu183
Thanks for this question, its interesting and I bet that if you asked 10 gardeners you'd get 10 answers.
Couch grass is a pain. Its long rhizomes propagate at an alarming rate, and once it starts, it can take years to remove. The best way is either to painstakingly dig it out or smother it (which is where your cardboard idea could work).
Couch grass, also known as twitch grass or quackgrass, can be a persistent weed in gardens and lawns. Here are some common issues associated with couch grass:
1. Invasive Growth: Couch grass is a fast-growing perennial weed with aggressive rhizomes (underground stems) that can quickly spread and form dense mats, outcompeting desirable plants for water, nutrients, and space.
2. Difficult to Eradicate: The deep and extensive root system of couch grass makes it challenging to eradicate manually. Even small fragments of the rhizomes left in the soil can regrow into new plants, making complete removal difficult.
3. Competition with Desired Plants: Couch grass can compete with desired plants in the garden, causing stunted growth and reducing overall plant health. It can be particularly problematic in vegetable gardens, flower beds, and ornamental plantings.
4. Disruption of Soil Structure: The dense network of couch grass roots can disrupt soil structure, leading to compaction and reduced soil aeration and drainage. This can negatively impact plant growth and root development.
5. Weakening of Lawns: In lawns, couch grass can quickly spread and form patches, creating an uneven and unsightly appearance. Its vigorous growth habit can weaken turfgrass and reduce lawn quality.
6. Difficulty in Control: Traditional weed control methods such as hand-pulling or hoeing may not be effective against couch grass due to its deep root system and ability to regrow from small root fragments. Chemical herbicides may provide some control but may also harm desirable plants if not applied carefully.
7. Persistence: Even after attempts at eradication, couch grass can persist in the garden for years, requiring ongoing management and vigilance to prevent its spread and regrowth.
8. Allelopathic Effects: Some studies suggest that couch grass may release chemicals into the soil that inhibit the growth of other plants, a phenomenon known as allelopathy. This can further hinder the establishment of desired plants in affected areas.
https://youtu.be/4WIDSCJ4o6M
Should I use weed killer for couch grass?
It all depends on how you're going to design your garden and whether you can control said weed killer when applying it. You may find it easier to use a spot weed killer on the couch grass a few weeks before you start layering your cardboard. If you use a deep enough no-dig layer of cardboard and compost, that may be enough to smother it out. Ground elder would be a different kettle of fish. You may even find a broadleaf weed and feed for the lawn helps weaken it, too, before starting the raised beds, even if you're getting rid of the lawn. That way, you can eradicate other perennial weeds, too!
In my experience, I'd use a spot weed killer on the most obvious bits, not a spray that drifts and causes drama with the ecosystem. I know that organic gardeners will be shouting, but sometimes you've got to use all the tools in your arsenal. In some cases, a suitable, well-applied weed killer is better than fighting with your garden; given your experience, it is a sound application.
Then, I would use twice as much cardboard for the no-dig bed as usual to ensure it's smothered.
Should you dig clay soil?
The quick answer is no, if you can help it. Clay soil is already claggy and lacking in air spaces, hence its fudgy texture. So I wouldn't waste time on your hands and knees compacting it or digging out couch grass. Adding a no-dig bed with lots of peat-free compost, leaf mould, or well-rotten manure will do wonders to open up the soil and break this clay texture.
https://youtu.be/SL8qCL_fGeM
Do let us know how you get on and keep us updated!
Lee Garden Ninja

Hi @cbu183

Thanks for this question, its interesting and I bet that if you asked 10 gardeners you'd get 10 answers.

Couch grass is a pain. Its long rhizomes propagate at an alarming rate, and once it starts, it can take years to remove. The best way is either to painstakingly dig it out or smother it (which is where your cardboard idea could work).

Couch grass, also known as twitch grass or quackgrass, can be a persistent weed in gardens and lawns. Here are some common issues associated with couch grass:

1. Invasive Growth: Couch grass is a fast-growing perennial weed with aggressive rhizomes (underground stems) that can quickly spread and form dense mats, outcompeting desirable plants for water, nutrients, and space.

2. Difficult to Eradicate: The deep and extensive root system of couch grass makes it challenging to eradicate manually. Even small fragments of the rhizomes left in the soil can regrow into new plants, making complete removal difficult.

3. Competition with Desired Plants: Couch grass can compete with desired plants in the garden, causing stunted growth and reducing overall plant health. It can be particularly problematic in vegetable gardens, flower beds, and ornamental plantings.

4. Disruption of Soil Structure: The dense network of couch grass roots can disrupt soil structure, leading to compaction and reduced soil aeration and drainage. This can negatively impact plant growth and root development.

5. Weakening of Lawns: In lawns, couch grass can quickly spread and form patches, creating an uneven and unsightly appearance. Its vigorous growth habit can weaken turfgrass and reduce lawn quality.

6. Difficulty in Control: Traditional weed control methods such as hand-pulling or hoeing may not be effective against couch grass due to its deep root system and ability to regrow from small root fragments. Chemical herbicides may provide some control but may also harm desirable plants if not applied carefully.

7. Persistence: Even after attempts at eradication, couch grass can persist in the garden for years, requiring ongoing management and vigilance to prevent its spread and regrowth.

8. Allelopathic Effects: Some studies suggest that couch grass may release chemicals into the soil that inhibit the growth of other plants, a phenomenon known as allelopathy. This can further hinder the establishment of desired plants in affected areas.

Should I use weed killer for couch grass?

It all depends on how you're going to design your garden and whether you can control said weed killer when applying it. You may find it easier to use a spot weed killer on the couch grass a few weeks before you start layering your cardboard. If you use a deep enough no-dig layer of cardboard and compost, that may be enough to smother it out. Ground elder would be a different kettle of fish. You may even find a broadleaf weed and feed for the lawn helps weaken it, too, before starting the raised beds, even if you're getting rid of the lawn. That way, you can eradicate other perennial weeds, too!

In my experience, I'd use a spot weed killer on the most obvious bits, not a spray that drifts and causes drama with the ecosystem. I know that organic gardeners will be shouting, but sometimes you've got to use all the tools in your arsenal. In some cases, a suitable, well-applied weed killer is better than fighting with your garden; given your experience, it is a sound application.

Then, I would use twice as much cardboard for the no-dig bed as usual to ensure it's smothered.

Should you dig clay soil?

The quick answer is no, if you can help it. Clay soil is already claggy and lacking in air spaces, hence its fudgy texture. So I wouldn't waste time on your hands and knees compacting it or digging out couch grass. Adding a no-dig bed with lots of peat-free compost, leaf mould, or well-rotten manure will do wonders to open up the soil and break this clay texture.

Do let us know how you get on and keep us updated!

Lee Garden Ninja

#3 · 16th May 2024, 1:30 pm

If you want to maintain the couch grass then you can see this: https://forum.charlesdowding.co.uk/community/topic/how-to-handle-couch-grass/qlik-sense

This approach really helpful for you.

Methods and advice for gardeners with clay soil: When it's somewhat dry, dig in the autumn and early winter. Clay soils frequently cannot be handled or walked on until mid-spring after being wetted by winter rainfall. Let the winter frosts do their thing and erode the clay.