What can you do about worm casts?

Helen Yemm the green-fingered guru solves Telegraph readers gardening problems. This week: a closer look at worms and the official start of spring.

The wonderful world of worms

Steven Walcott is amazed that his lawn, which has spent an extraordinary amount of time in the past month or so under water, is still alive and, more extraordinarily, he says, so are the worms that must have had a really hard time of it. He expected all the worms to have drowned, and that the only upside to look forward to was that the wet winter flooding would have meant that his silty, muddy but still-alive grass would not be peppered, as it usually is during the winter, with irritating worm casts. But lo, within a couple of weeks of the last inundation, the casts are back. How do worms survive against all the odds, he muses in his email? And is there anything he can do about worm casts that constantly mess up his lawn?

In the absence of gills or lungs, earthworms “breathe” rather ingeniously through their skin as long as they stay constantly moist and hang out in soil that doesn’t dry out (thus they disappear downwards in summer). They can even survive for several days in flooded ground, absorbing the oxygen present in water through their skin. They also, it would seem, have an inbuilt ability to sense when rain or flooding is likely to occur, and move themselves (albeit slowly) to higher ground, returning when the coast is clear. Many earthworms will have perished, it is true, in land that has been continuously under water for weeks, and I understand it may take as long as six months for the worm population to recover in the seriously flooded areas.

Gardeners should definitely regard earthworms as the Good Guys out there. By their activity, they gently churn the topsoil, dragging organic matter down into it on which they feed, so helping to make humus, which is vital to plant life. As they go, they create channels that help with drainage and aeration, ensuring that plant roots (which also need oxygen) thrive. They are thus absolutely vital to the health of our soil, and their significance to life on earth is of positively bee-like magnitude. As Charles Darwin himself noted: “It may be doubted whether there are many other animals which have played so important a part in the history of the world, as have these lowly organised creatures.”

However, as Steven points out, there is a niggling downside to earthworm activity for lawn-proud gardeners, namely the proliferation of little piles of fine silty soil that they leave on the surface – completely unnoticeable in flower beds, but irritating on lawns because they so easily become flat discs of mud if trodden on. In dryer spells of weather during spring and autumn, when worms are at their busiest, casts can of course be swished off the lawn with the aid of a broom or scattered using a flat-tined plastic lawn rake turned on its back. If that isn’t good enough, to a great extent worms can be persuaded to move off lawns by the application of various deterrents, the latest of which to adorn the shelves in garden centres is CastClear (CastClear.co.uk, from The Lawn Company Ltd, 0871 234 3482). Containing organic sulphur and amino nitrogen, it is applied via a sprayer, and while it in no way harms the worms, they dislike working their way through soil that has been treated, so in effect the CastClear does shoo them off to play elsewhere.

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