All gardeners spend the warm, wet Welsh summer doing battle with slugs, but organic gardeners shouldn’t resort to slug pellets to save their plants as they can pose a risk to other wildlife. This article gives some ideas for natural alternative solutions to try instead. There are thirty different types of slug in Britain. The most common, and those whish do the most damage, are the grey field slug, the garden slug, the keel slug and the black slug. The grey field slug, Deroceras reticulatum, was once prescribed as a cure for consumption and either swallowed live or boiled in milk.
A single slug can lay up to five hundred eggs each year. They can over-winter and become active again as soon as conditions become mild and damp in the spring. Slug pellets are cereal chunks containing poison, such as metaldehyde. The cereal bait can also be attractive to other wildlife and pets. There is also the danger of a predator, such as a hedgehog, eating poisoned slugs. Metaldehyde has been reported as affecting the fertility of songbirds. The pellets can therefore cause injury or death to other animals, even if stored and used correctly. Slug pellets are banned under Soil Association standards.
Prevention is Better than Cure
Organic gardeners should encourage natural predators so that the slug population is kept under control. Ground beetles are very useful as they feed on slug eggs as well as the slugs themselves. Garden birds such as blackbirds and song thrushes will eat considerable numbers of slugs, as will frogs and toads. A hedgehog can eat hundreds of slugs a night. Slowworms, spiders and harvestmen can eat small slugs. If you keep chickens or ducks, you’ll find that they also enjoy a meal of mollusc. Hedges, log piles and compost heaps all provide habitats for these predators – unfortunately, they can also give cover to slugs…
In the vegetable patch, some crop varieties are more attractive than others to slugs. Garlic, onions and chives between crops might help deter them. Planting a lavender bush border and keeping the patch weeded might also help. Slugs thrive in damp gardens with plenty of vegetation to provide cover and aid movement. Adding sand to the soil in ‘sluggy’ sites can help improve drainage. Slugs find fine, firm soil more difficult to cross and there will be fewer air spaces that slugs can use as shelter.
Flowers that seem less attractive to slugs include busy-lizzies, foxgloves, hollyhocks, lavateras, forget-me-not, alliums, rosemary, wallflowers, lavender, phlox, columbine, snapdragons, geranium, tulips and hydrangea. Water your garden in the early morning rather than in the evening, when slugs are just becoming active, as the moisture attracts them and helps them move around.
There are various methods of slug control that gardeners employ, with varying degrees of success. On a small scale, traditional beer traps are very effective at drowning slugs, but other invertebrates might also be caught. Traps can be made easily by recycling large, lidded, plastic yoghurt pots. Wash the empty pots and dry. Cut two slug-sized holes on either side, 1 cm down from the rim. Sink into the soil to the level of these holes. Fill with beer (or grape juice) to a depth of 2cm. Replace the lid to stop rain getting in. Empty each morning and top up the liquid.
Barrier methods can be used to stop slugs getting to plants in pots. Petroleum jelly can be smeared on the rim or copper tape stuck around the edge. This has a small electrical charge that repels slugs. Broken eggshells, ash and salt can also be effective barriers. Slugs are said to dislike the smell of pine, so borders could be made with pinecones.
Oatmeal and bran are very appetising to slugs, but kill them. Horse bran can be bought cheaply in large sacks to spread over vegetable patches. Other methods are more direct and immediate. Mowing the lawn at dusk will cut up slugs. Night patrols with a kitchen knife or scissors and a bucket for the carcasses can be very effective if you have the stomach for the job! Competitive small children could be given pocket money for the number of slugs they collect and drown.
Nematodes, such as Phasmorhabditis hermaphrodita, are a biological control agent that can be very effective in reducing an established slug population. The eggs are watered into the soil where they hatch, search out and infect slugs with bacteria, preventing them from feeding. The slug dies within ten days while the nematodes reproduce inside the body, ready to find new victims.
In the future, a wildlife-friendly slug pellet might be available which will be safe to use in gardens. The Research Institute for Organic Agriculture in Switzerland is developing a pellet based on iron phosphate, which is not toxic to animals. This might finally be the answer we’ve all been waiting for!