Should you try to control worm casts on your lawn?

By | 07/02/2018
Worm cast on a grass lawn

On your lawn, you may see tiny mounds of soil appearing on the surface. They crop up in random places all over the lawn. They most often appear in the autumn or winter, but can crop up at any time of the year. These are worm casts.

An earthworm on a lawn
An earthworm

Worm casts are created by earthworms. These worms consume and digest organic matter in the soil. They then expel it from their gut onto the soil surface. This creates the coil of smooth soil which we call worm casts.

In the UK, worm casts are created by three different species of worms. The lob or common worm (lumbricus terrestris), The grey worm (aporrectodea calignosa) and the black-headed worm (aporrectodea longa). The lob worm is the most common worm cast creator. It only comes out at night or during periods of heavy rain.

On your lawn at home a worm cast can be squashed underfoot making a muddy patch on the grass. The mud can be smeared on the patio or stepped on and trodden indoors, causing a mess. A squashed worm casts is also a perfect germination patch for a weed seed.

Worm casts can be a nuisance in the lawn care industry. Especially on fine turf lawns such as golf courses and bowling greens. These rely on a smooth surface to roll a ball on. A golf green dotted with worm casts can become unplayable. Worms soften the surface and their casts blemish the green.

It is frustrating that the high nutrient content and good soil required for fine turf is a haven for earthworms. The better your lawn, the more difficult the problem of worm casts can become. Green keepers have battled with earthworms for decades.

Should you try to control worm casts on your lawn?

Worm cast close up
A worm cast

On a lawn at home, worm casts are less of an issue. The longer grass and less reliance on a flat surface make worm casts less problematic. In most domestic lawn care situations, I discourage trying to control worms. Worms bring too many benefits to soil and the general ecology of your garden. Trying to control them may only bring further problems.

If it does bother you though, what can you do about it?

Natural ways to control worms casts

  1. Leave your lawn longer. A longer grass brings a healthier lawn. Blemishes in the soil surface tend to not be a problem if the grass leaves are longer. Especially in the winter. Keep your mower blades high (at least 30mm) and the worm casts will be less of a problem.
  2. Reduce the worm food source. Keep the leaves off your lawn in the winter. Also make sure you remove the grass clippings when mowing. Reducing the amount of organic matter on your lawn will reduce the amount of worm activity in the soil.
  3. Improve the drainage. Worms tend to put up more casts and seem to be more active in wetter soils. Improve the drainage in your lawn and you will reduce your worm problems.
  4. Brush casts away when they appear. If you see worm casts appearing, use a stiff broom to brush them away. This will distribute the nutritious worm casts soil and remove the problem. This is best done before mowing and when the casts are dry.

Chemical control of worm casts

  1. Carbendazim is a worm control used by professionals. It suppresses worms by keeping them lower down in the soil. In my experience it can also kill worms, which is why I no longer offer the treatment. Carbendazim is not available to the general public. Some lawn care companies will apply worm controls so get in touch with your local operator. There are rumours that it is in danger of being added to the banned chemicals list. So it may be withdrawn at any time. Edit: It was confirmed as withdrawn in 2016.
  2. There are some worm control products which are available for home use. These are usually based on sulphur. Sulphur lowers the pH of the soil, making it more acidic. This tends to discourage worms. Attempting to adjusting your soil pH can bring mixed results. At worst it can cause other turf problems. It is best to conduct a soil test and try in small amounts if you wish to try this route.

Worm cast control in summary

Unless you are aiming for a smooth surface, trying to control worm casts in your lawn is unnecessary. Try to reduce the number of casting worms naturally and maintain your lawn correctly. You will find that you will learn to love the humble earthworm. They are your friends in your garden.

Further reading

12 thoughts on “Should you try to control worm casts on your lawn?

  1. fedup

    I think worms to be honest a royal pain! We took up paving, dug up, removed sand, rubble etc and put a new lawn down 3 years ago, garden was concrete and both sides of our property their gardens are still concrete. The first year worms made it lumpy and uneven, hard to mow and have to be careful walking on it so not to lose your footing. The 2nd and 3rd year they’ve destroyed it completely. I don’t know where they came from in so many numbers to be honest! The last 2 winters it’s 90% pure mud and grass gone and at night there are hundreds of large worms come up to lay and eat the grass as well as plants in my flowerbed. I reseed several times in the spring and summer at a cost, but I think after another winter of mud everywhere, I will give up and lay a fake lawn. Such a shame there’s nothing available professionally to help control the numbers as fake lawn is the pits.

  2. Robert

    Our lawn in UK (Surrey) was utterly destroyed by worms. We had a new soakaway and French drain put in for good measure. The old subsoil was awful – about 1 inch of topsoil plus huge metre squared lumps of concrete and asbestos! It used to be a farm in once and the house dates back to the 1750’s when it was a coach house. Anyhow, we managed to put about 5 inches of quality topsoil and best quality turf over the new drainage system having removed all the dreaded asbestos and as much of the concrete as we could. The new lawn was totally and I mean completely infested with worms within 3 weeks, and 6 months later is utterly ruined – more mud than grass. We had a guy put something like cast clear on it 4 times and the worms receded a little. He said he’d only once in 20 years ever used it more than once. The worms just came back and wrecked the entire lawn. I don’t think anything except napalm would stop these guys.

    1. Kris Lord Post author

      Are you sure they are worms and not Leatherjackets? Worms don’t eat grass so I’m not sure how they could “destroy” a lawn, even in large numbers.
      Try seeding in future, the grass will make its own way then. Your turf probably died of other things.

  3. Denise Swindlehurst

    Can worms killed using a chemical be harmful to birds who eat them?

    1. Kris Lord Post author

      Yes, potentially.
      One of the many reasons worm controls have been banned by regulators.

  4. Jamie

    I put a new lawn down last year, it’s really patchy could this be down to the worm casts.

    1. Kris Lord Post author

      It could be. Could be a number of other things though.
      A bit of investigating will help find out what it might be.

  5. Sue Moorhouse

    Thank you for your advice. I love worms, so will just brush the casts when they are dry, leave it longer and aerate my lawn. It was newly turfed, so I’m assuming the soil is full of worms as it was concreted before.


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