IN MOST parts of the world, earthworms are seen as the gardener鈥檚 friend because of the many ways they improve the soil. Worms feed on decaying organic matter and their faeces contain soil nutrients, such as nitrogen, phosphorus and potassium, in forms that are easier for plants to take up. Their tunnels also improve drainage and give a lighter, more airy structure to soil.
Ecologists may use the number of worms in a patch of earth as an indicator of whether soil has a good pH, sufficient organic matter and isn鈥檛 too compacted. Gauging this in a standardised way involves digging multiple pits, which may be unappealing to home gardeners. I like to do an informal check every so often, by turning a few spades of soil onto a tarpaulin, even if just to practise my .
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In healthy soil, the number of worms in a single pit that is 25 centimetres square and 10 cm deep could range from just a few to over 50, with the number varying with the season and moisture conditions, says Keiron Brown of the Earthworm Society of Britain.
Another way to assess your worm population is . Add 25 millilitres of mustard powder to 750 millilitres of water and shake well, then pour onto a small, bare patch of soil. Within about 10 minutes, any worms that come into contact with the liquid should be at the surface. The solution isn鈥檛 harmful, but the worms do find it irritating, so, to be kind, you could wash them with water afterwards.
In temperate regions like the UK, there are three main types of worms. Epigeic earthworms usually live on the surface among dead leaves. They tend to be dark red, matchstick-sized and fast.
Endogeic earthworms are pale or greenish and live in the top 30 centimetres or so of the earth; they usually make horizontal burrows. Anecic earthworms are dark red and tend to be the longest; they make vertical burrows that can be 2 metres long and are invaluable for mixing up surface and deeper soil layers.
It is possible to buy worms to add to your garden, but it is best to entice them naturally by leaving any dead plant material, or leaf litter, on the soil and, if necessary, adding more organic matter, says at the Natural History Museum in London. This doesn鈥檛 even need to be dug in 鈥� if you lay it on top of the soil, the worms will pull it down.
The ecosystem engineering powers of these animals are evident in the forests of Canada and the northern US, which today lack most species of earthworms because they died out there during the last glacial period. These forest floors have deep layers of decaying organic material. But, in areas where earthworms have been accidentally reintroduced, there is noticeable loss of these layers, which is bad for insects that make their home in this rich material.
What you need
Organic matter, such as leaf litter, for adding to the soil
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