Worms are beneficial in the garden as their burrowing activities improve the aeration and drainage of the soil. They also improve the nutrient content of lawns and turf by pulling leaves and other organic matter into their tunnels, passing it through their digestive system, in turn delivering a nice compost. However in spring and autumn when the soil is warm and moist, certain species of earthworm can be the scourge of the lawn turf owner, depositing their muddy casts on the lawn surface. If casts are smeared onto a lawn whilst still moist, these muddy casts can ruin the visual appeal of turf. Worm casts may also contain weed seeds. The bare patch that a smeared cast creates is an ideal space for these seeds and other air borne weed seeds to germinate.
Dealing with worm casts
Avoid mowing or walking on casts whilst moist, as this will smear the casts into the lawn surface. Allow the casts to dry out when they will become much lighter brown in colour and crumble when squashed between thumb and finger. The casts can then be easily flicked away from the surface using a besom broom or an upturned wire rake, leaving only a slight blemish on the lawn turf rather than a large smear.
Deterring worm activity
Although deterring worm activity will reduce the positive effects that they provide, in some severe cases this can be a necessary sacrifice. There are a number of ways in which worms can be deterred; the easiest solution is to reduce the amount of food available for them. This is best done by reducing the amount of decaying organic material in the lawn surface through removal of leaf litter in autumn, the collection and removal of grass clippings throughout the growing season and a programme of regular scarification. It is also possible to alter the soil characteristics to create conditions that they dislike. Earthworms seem to be discouraged from lawns with a high sand content, probably due to the lower moisture content and abrasiveness of the sand particles. Therefore applying top dressing with a high sand content is one option. Earthworms also appear to dislike soil with a low pH and so the use of acidifying materials in fertilisers and iron sulphate can reduce casting problems. It is worthwhile to note that there are no longer any lumbricides approved for use on garden lawns. To sum up earthworms are helpful in keeping the soil healthy, however at certain times of the year in extreme cases their presence can affect the appearance of the lawn. This can be dealt with if necessary with a little time and effort.
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