After rainfall, lawns on clayey soils are often littered with numerous piles. But what is behind this phenomenon and how can you prevent the heaps on the lawn?
Anyone who walks across the lawn in the fall often finds that the earthworms were extremely active during the night: 50 small heaps of worms per square meter (1.2 yd²) are not uncommon. The most unpleasant thing is that the mixture of loamy soil and humus sticks to your shoes in damp weather. The worm piles occur mainly after rainfall on dense, mostly loamy soils. Earthworms leave the deeper, wetter soil layers and stay just below the soil surface. Here they do not leave their excreta in their feeding tunnels as usual, but push them to the surface.
Why rain worms move up in the soil has not been fully explained to date. It is often read that the animals cannot absorb enough oxygen in waterlogged soils and therefore escape into the airier soil layers. However, studies have shown that earthworms can survive for months even in flooded meadow soils and even reach particularly high population densities here. This behavior can also be observed if the soil is made to vibrate slightly. Therefore, it is now assumed that this is a natural escape instinct triggered by slight vibrations of the soil, for example by burrowing moles, the earthworms main enemies, or by raindrops pattering on the earth. Since a dense cohesive soil transmits the vibrations better than loose sandy soil, this phenomenon seems to be more pronounced on clay soils.
Many worms, healthy soil
The good news is that if you have lots of worm piles on your lawn, you can consider yourself lucky, because the dense earthworm population shows that the soil is healthy and provides good living conditions for the useful waste recyclers. After all, the amateur gardener also benefits from this, because the worms have an important function: they loosen the soil with their thin tunnels, pull the organic waste lying on the surface into the soil and digest it into valuable humus. In this way, a soil rich in earthworms becomes looser and richer in humus from year to year and produces higher yields. So the heaps of worms are actually a reason to rejoice.
How to reduce the piles of worms
If you are still bothered by them, you should not actively fight the worm population in any case, but make sure that the soil under the lawn becomes more permeable in the long run. This can be achieved, for example, by so-called aerification with a special wide fork, but this is very strenuous and time-consuming. Instead, it is better to scarify the lawn in the spring. Then apply a two to three centimeter (0.8 to 1.2 in) layer of coarse building sand.
The lawn is not harmed by this thin covering, as it grows through it very quickly, rather the opposite: if you repeat sanding the lawn every year, the top layer of soil becomes more permeable over time, dries out again more quickly after rainfall, and the earthworms retreat to deeper layers, where they also leave their droppings.
By the way, the worm piles usually disappear by themselves during a heavy downpour, as they are simply washed away. In sunny weather, simply wait until they are thoroughly dry and then you can easily level them with the back of the lawn rake or a lawn rake. Since worm humus is a prime source of nutrients for garden plants, you can also collect it with a small shovel, then dry it and use it as a natural fertilizer the next year.
If all this is not fast enough for you, you can simply collect the earthworms at night in wet weather and relocate them. To track them down, it’s best to use a flashlight that’s been taped with red foil, because in white light, the worms immediately take flight. You then collect them in a bucket and release them in another place in the garden, where the heaps of worms do not disturb further.