For the last month, our irrigation reservoirs have been rimmed by a black mass of writhing tadpoles. I reckon there are over a million in the one I swim in, even after the carp have feasted. Last week they got their legs and this week they are off; the ground around the ponds is heaving as they go in search of their first terrestrial meal. Facing this hungry biblical plague, slugs have no chance. It will be two years before the toads return to breed, by which time they’ll have made a home on the waterless hill half a mile away.
“What we do about slugs” is always the visiting gardener’s top question on our organic farms. The answer, with the occasional exception of our polytunnels, is nothing; they aren’t a problem for our field crops. I know you will find the occasional slimy surprise in our lettuces and our sprouts are often scarred (which we hope and assume you can live with), but I cannot remember ever seeing any organic crops suffering significantly. Most conventional potato growers will routinely apply vast quantities of slug pellets and still have substantial damage. Likewise, slugs can be a huge problem in winter wheat and barley even after applying pellets, but almost never when the ground has been organic for three years or more. The reason is undoubtedly that our soils, free from pesticides and synthetic fertilisers, are teeming with life looking for a meal; toads, frogs and carabid beetles like to munch on slugs, nematodes will parasitize them, and there are almost certainly many other predators and pathogens. No-one makes money from their activity, so this unglamorous part of ecology hasn’t been studied much.
The principle of organic farming is to find balance; the population of every indigenous pest (except Homo sapiens) is regulated by predators and pathogens. It doesn’t always work; sometimes you have to encourage them a little (e.g. flowering plants to foster the lacewings and hoverflies that control aphids), but with slugs all you have to do is spare the soil those toxic chemicals, and soil ecology will do the rest. Annoyingly I know this approach does not work in a garden; I suspect there is just too much cover for the slugs to retreat to. If you can handle the poo and keep the foxes away, get a duck.
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