Prolific during the wet winter season, worm casts can cause concern for the amateur gardener with the sudden appearance of small heaps of soil that pop up on the surface of the lawn. However, worms are not all bad news for the gardener, in fact they are often considered the gardener’s best friend. So what exactly is a worm cast and why do so many crop up on our lawns over wet periods?
Worm casts are small mounds of soil, coiled in appearance, that emerge on lawns and in flowerbeds mainly from September to May when the soil is wet. Casts are the byproduct of earthworms that feed on dead plant materials (while ingesting small amounts of soil). The worms digest the goodness from the food before extracting their waste product up through the soil as they travel through, cleaning their burrows. Worm casts will be abundant on clay soil and soil that is very wet – normally the wetter the soil, the greater the worm cast activity. There are numerous species of worms that cast underground with no cause for concern for the gardener, and just a few that tunnel above ground to cast. It is these species that can cause gardeners problems with their lawns.
There are 5 varieties of casting earthworms found in British soils. Generally speaking, the presence of earthworms in soil is a real plus, both for the gardener and the nutritional value of the soil. Worms, during their daily activities, create tunnels which naturally aerates the soil and also helps with drainage. Plant’s roots also benefit from the actions of worms, as the worm’s underground movement allows oxygen to reach the roots, encouraging stronger healthier growth.
The biggest problem for lawns with an abundance of worm casts is that the casts are usually slimy in texture (as is the nature of a gut byproduct!), and can be easily trodden in and spread over the surface, creating a muddy lawn that looks unappealing and can also be more susceptible to moss and weeds.
Try to keep off the lawn as much as possible to avoid squashing the worm casts and transferring the mud across the grass. When the weather improves the casts should dry out and can either be brushed across the lawn with a broom, or broken up with the back of a rake. Never break the worm casts up while they are still wet, as you will end up spreading them over the entire lawn area, with disastrous results. Worm cast control products are also available which create a barrier that the worms aren’t eager to pass through, and so the worms remain deep in the soil rather than cast above ground. These products are completely safe, and do not cause any harm to the worms – simply apply the product in September or October for worm cast control over the wet winter months.