With the spring season approaching, you might start to see small, coiled piles of soil scattered across your lawn. These are known as worm casts, a byproduct of earthworms processing organic material underground.
While they indicate healthy soil and a thriving ecosystem, they can be a nuisance for those who strive for a pristine lawn. Cheryl Harper, Managing Director of Greensleeves Lawn Care, explains everything you need to know about these muddy mounds and how to effectively manage them.
Worm casts are the tiny heaps of soil that earthworms leave behind as they feed and enrich the ground with nutrients such as nitrogen, phosphorus, and potassium. This process is beneficial for the soil and enhances grass health, but the resulting mounds can cause issues, particularly for those with ornamental lawns – as worm casts can smear underfoot or when mowed, creating uneven patches that encourage moss and weeds to spread.
Earthworm activity is at its highest during the cool, damp conditions of autumn and early spring. As the weather warms up and rain softens the soil, worms come closer to the surface to feed, leaving behind more visible casts.
For that same reason, we tend to see them less during hot summers or freezing winters, when they tend to retreat deeper into the ground.
While it’s impossible to completely eradicate worm casts, managing them is entirely possible with the right approach: Wait for the lawn and mounds to dry, and then use a soft rake or stiff brush to gently brush them away, preventing smearing and soil compaction.
During peak worm activity, raising the height of your mower can also help conceal the mounds – so keeping your grass longer makes them less noticeable and reduces the damage caused by mowing over damp soil.
Keeping your lawn free of organic debris, such as fallen leaves or grass clippings, can also make it less appealing to worms, and compacted soil often forces worms to the surface, so aerating your lawn can help by improving oxygen flow and drainage. This creates a healthier environment for your grass while encouraging worms to stay below ground.
For a more long-term approach, adjusting your lawn’s soil conditions can make a significant difference. Worms thrive in neutral to slightly alkaline soil, so slightly acidifying the ground with sulphur-based products can discourage their surface activity without harming the grass.
Similarly, reducing watering frequency and ensuring good drainage can create conditions that are less inviting for worms while still supporting healthy grass growth.
