They may make you squirm but wriggling earthworms are an important part of the garden ecosystem. Not only do worms help to increase soil aeration, nutrient cycling, water movement and plant growth, but they are also a valuable food source for many animals.
The only downside? Those muddy coils that the worms deposit all over your pristine lawn when they tunnel into the ground. If your lawn is plagued by a sea of earthworm castings, keep reading to find out how they got there, how you can remove them, and how to stop them from coming back.
Are worms good for soil?
Earthworms are one of the most important factors in ensuring good soil health. Worms ingest soil as they tunnel into the ground and excrete most of it, along with a host of beneficial nutrients and minerals, onto the surface of the soil. These miniature coils of earth pop up all over lawns, sports fields and golf courses and are known as worm casts (in other words, earthworm poop).
The goodness in the worm casts comes from decomposing vegetation like leaves and plant roots. This nourishing mix provides essential nutrients for plants and also provides a food source for soil-dwelling microorganisms.
Worm castings are so beneficial to the soil that you can even buy potting soil mixes with added casts. As well as the nutrition boost that worm mounds provide, worm tunnelling effectively aerates the soil. Although small, earthworms are impressive burrowers and can tunnel as deep as 6.5 feet into the soil.
What are worm casts?
Worm casts are the final product of worm digestion, also known as, worm poo. Because worms have such voracious appetites and can consume up to a third of their body weight in one day, they produce vast amounts of poop.
This waste gets pushed up through to the surface of the wormhole, creating a cast. It’s a similar process to the formation of a molehill, only the soil comes out of the worm’s bottom instead of being pushed out of the way by digging feet. The deeper the worms burrow, the bigger the worm cast becomes.
What do worm castings look like?
Worm casts look just like you would expect, long, brown coils of soil and you’ll find them randomly dotted over the surface of your lawn. They can be distinguished from the fine piles of soil brought up to the surface by other lawn-dwelling animals, such as ants, mining bees and moles, by their compact structure and coiled appearance.
Why you’d want to remove worm castings from your lawn
As nutrient-dense as worm castings may be, there’s no doubt that the coils of muddy soil left by earthworms are unsightly, especially if you have an earthworm infestation in your lawn. Worm castings on the lawn are a familiar sight in gardens and you’re most likely to notice them in autumn and winter.
Large quantities of soil pass through the worms as they tunnel, mixing with secretions from their digestive systems before being excreted onto the lawn. The casts are soft and squishy and the more you have on your lawn, the more of a muddy mess it can quickly become.
Worm casts aren’t just an aesthetic problem, if you have excessive piles of soil, they’re likely to get squashed, covering and suffocating grass and providing areas of nutrient-rich bare soil for weeds to take hold.
Worm activity will increase during wetter autumn and winter periods, and decrease in hot weather and freezing conditions as the surface of the ground becomes impenetrable. Extensive worm tunnelling near the surface of the grass can affect the structure of the soil, making it spongy and soggy and creating difficult mowing conditions. You’re more likely to have a worm cast problem if you have organic-rich or heavy clay soil.
How to get rid of worm casts
Although worm castings contain beneficial nutrients, these nutrients will be better absorbed when they are worked into the soil, rather than sitting in mounds or flattened bumps on top of the lawn.
Earthworm damage to lawns can be a real problem but there are a few ways to remove the worm casts:
1. Sweep them away
This is the quickest and easiest solution, but you’ll need to wait for a few days of dry weather before you start sweeping. If you’re able to brush the castings into a dustpan, you can dry them out, crumble them up and add them to your potting soil.
2. Scoop them up
If you only have a few worm casts to deal with, you can simply scoop them up using a trowel. Although sweeping and scooping won’t solve the worm cast problem in the long term, it will help to preserve the appearance of your lawn and protect your grass throughout winter.
3. Amend the soil
An effective way to reduce the number of worm casts is to apply a non-pesticidal, organic soil amendment product such as NutriFlo Casting or CastClear. As well as improving overall turf health, it will alter the surface of the soil, making it less appealing to the worms and discouraging them from casting there.
How to stop worm casts on your lawn
Worms in the soil do more good than bad, but the casts they leave behind are unsightly and potentially damaging to the lawn. The best way to stop worms from tunnelling near the surface of your lawn is to deter them.
- Good lawn hygiene will make a big difference to the number of casts that appear in your garden. Make sure you remove fallen leaves and other debris regularly. Leaves form a large part of a worm’s diet and they’ll pull leaves into their tunnels.
- You can prevent worm casts from forming in the first place by applying a pesticide-free worm cast treatment. These products usually contain a specific mix of nitrogen, ammonia, sulphur trioxide, calcium and iron and work by deterring the worms from penetrating the upper layer of soil. Although organic soil amendments won’t kill the worms, they will keep them deeper in the soil.
- Apply an iron-based lawn fertiliser throughout the year to help deter worms. Although you might be tempted to buy a worm killer for lawns, the only products to do so contain insecticides and we don’t advocate their use.
- Don’t overwater. The more moisture there is in the soil, the easier it is for worms to tunnel their way through. Worms will head deeper into the soil if the top layer is dry so keep that in mind during drier spells.
Do worms eat grass?
Although worms in grass can cause damage to the lawn through the casts they leave behind and their extensive tunnels, they don’t generally eat grass, preferring to chomp on the thatch layer below or old grass cuttings.
How can I get worms out of the ground?
One way to deal with worm casts is to try to trap and remove the worms yourself. It could work as a quick fix but there are likely many hundreds of worms under your lawn so you could be repeating this process all winter.
A good trick to get worms to come to the surface of the soil is to put a large, damp piece of cardboard on the ground overnight. In the morning, there will be many worms under the card – this is a great method if you’re collecting worms for a wormery or fishing bait.
Although the presence of worms in the soil is generally good, an excessive number of worm casts is not. If you’re able to prevent worms from casting in the first place, your lawn’s appearance will benefit hugely.