Ignoring worm casts on your lawn by squashing them flat with your mower will create an uneven surface, smother existing grass and provide an ideal seed bed for weeds to grow in. In recent years products to control casting worms have been withdrawn.
However, it is common knowledge and in the public domain that casting worms do not favour acidic soils. So when a soil acidifier is applied to the lawn they will burrow deeper into the soil – without coming to any harm – reducing casts on the surface.
It may well be necessary to make two or three applications in the autumn and spring, especially if there is a lot of vegetative matter (thatch) in the soil and/or the lawn is growing on an alkaline (chalk or limestone) soil.
Prevention is always better than cure and we recommend that an application of Sulphurlawn Chips or Spray-on is made before the casts become a problem.