I suspect that many of us, at some point, ask for a bit of help in the garden. How aware are we, though, of the help that is already there? Worms are so familiar that it’s easy to take them for granted, but look at the work they do on the vegetable plot and you may never want to use a rotovator again.
We all know that a healthy compost heap is writhing with worms, working their way through the kitchen and garden waste to help create organic matter to feed our soil—these are mostly brandling worms, recognised by their red, stripy appearance—but I’m talking about the worms which, if your soil is good, you’ll find in large numbers throughout your vegetable plot. How useful are they?
Well, first, they’ll be munching on leaf fragments and other plant debris that accumulate on the soil surface. Research indicates that, having passed through worms, these bits and pieces are broken down more easily by microbes. Result? Humus! That black gold beloved of all organic gardeners is produced more quickly with the help of worms than by microbes alone.
With worms having little to do but eat, they shift a surprising amount of material. One study on forests came to the conclusion that worms buried over 90% of the plant debris left on the soil surface. Another indicated that an impressive forty tonnes of soil per hectare were brought to the surface in worm casts in the course of a year.
This is great news as worm casts tend to be very fertile, holding more calcium, iron and phosphorous than the soil around them. They also contain significant amounts of nitrogen and help to stabilise carbon, reducing the release of carbon dioxide from the soil. The small particle size in the casts means they can even hold more water.
The net result is that more organic matter and nutrients are incorporated into your soil, minerals from below are brought up into the root zone and your veggies have access to more moisture.
Of course, worms also burrow, and not all in the same direction. Epigeic species burrow in the litter on the soil surface; anecic species live in vertical burrows that can descend several feet. Endogeic species burrow below the surface in horizontal or random lines. Aristotle described worms as "the intestines of the soil", which is a good way to regard the passages they create. Burrows open up the soil to air, bringing oxygen to plant roots, and create pathways for water and roots. The presence of earthworms has been shown to have a notable effect on the amount of water a soil can hold and on how fast it sinks in.
Not all worms are good
It’s possible that by now a few of the scientists among you are in danger of apoplexy, so I should add that you can’t assume that all worms do all of the above. The Encyclopaedia Britannica numbers worm species around the world at over 1800 and they’re not all doing the same thing. While some open up the soil, for example, others actually compact it. Surprisingly, bringing earthworms into an environment isn’t always a good thing—species introduced to otherwise wormless North American forests are causing problems by destroying the deep surface litter.
However, in normal garden circumstances, you don’t have to start rounding up worms and quizzing them on their usefulness. Barring an exception like the New Zealand flatworm, which is appearing in the UK, you can assume that all your garden worms are playing their own particular part in the creating nutrient-rich soil to feed your delicious veggies.
Looking after worms
Given their activities, it’s a good idea to encourage as many as possible to hang out in your soil, so my first suggestion is to dump the rotovator. Agricultural research has shown that the more soil is tilled, the fewer the worms are in it and, despite rumours to the contrary, worms cut in half do not grow into two worms. It’s true that, in some circumstances, one half might survive, but on the whole you can assume that a bisected worm is a dead worm.
Digging also presents a clear and present danger to them, though on nothing like the scale of a rotovator, and worm safety is one of the reasons I’m a great advocate of No-Dig beds which leave soil undisturbed. If you must dig, using a garden fork rather than a spade is less likely to damage worms.
Bear in mind, too, that worms eat organic matter and, if supplies drop off, they will vote with their contractile tissue and move elsewhere. They also need moisture, which is why in dry weather you’re likely to find them in the damp soil under stones or wound into a tight ball. It’s their way of protecting themselves from heat and dryness until conditions improve.
The best answer to keeping them happy is to look after your soil. Ensure that it’s well fed with compost and spread with mulch, and don’t dig unless you have to. Not only will it be good for your plants, but the organic matter and improved water retention will make the worms want to call your garden home.
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By Helen Gazeley