Slugs and snails

Slugs and snails cause more complaints from gardeners than any other animals. They cannot be eliminated from a garden, and most methods sold or recommended for the purpose have little evidence behind them. What works is protecting the plants that are actually at risk, at the time they are at risk.

Not all are pests

Around forty species of slug live in Britain, and only a handful do significant damage to garden plants. Many feed mainly on dead and decaying material and are part of the process that turns it into soil; the large leopard slug also eats other slugs. Slugs and snails are food for hedgehogs, frogs, toads, slow-worms, ground beetles, song thrushes and blackbirds. In 2022 the Royal Horticultural Society announced that it would no longer class slugs and snails as pests.

What is at risk

Damage is concentrated in spring and in mild, wet weather, and on soft growth: seedlings, young transplants, and the emerging shoots of hostas, delphiniums, lupins and dahlias. Lettuce, young beans and courgettes, strawberries and potato tubers are the main casualties in the vegetable plot. Established shrubs, grasses, ferns and plants with tough, hairy or aromatic leaves, such as lavender, hardy geraniums and foxgloves, are largely left alone.

Slug pellets

Pellets containing metaldehyde were withdrawn in Great Britain because of the risk to birds and mammals, and their outdoor use has been illegal since 31 March 2022. Old stock should not be used; local councils advise on disposal.

The pellets that remain on sale contain ferric phosphate, which is also approved for organic growing. They are scattered thinly, following the label, around vulnerable plants only. Slugs that eat them stop feeding and die underground, so few bodies are seen.

Nematodes

A biological control is sold in the form of microscopic nematode worms that infect and kill slugs. The product is bought fresh, mixed with water and applied to moist soil with a watering can, once the soil temperature is above about 5°C. It acts for roughly six weeks. Nematodes work on slugs living in the soil and have little effect on snails, which spend less time below the surface.

Barriers and home remedies

Copper tape, crushed eggshells, sharp grit and wool pellets are all widely recommended as barriers. When the Royal Horticultural Society tested them in garden conditions, none reduced slug damage. The RHS summary of the evidence is given in its advice on snails.

Beer traps and upturned grapefruit skins do catch slugs, without any proof that they lower damage to nearby plants. A trap sunk with its rim level with the soil also drowns ground beetles, which are slug predators; leaving the rim 2 cm proud avoids that.

Salt kills slugs but also damages soil and plants, and is not recommended.

Methods that help

• Raising plants under cover: seedlings grown on in pots and planted out as sturdy young plants survive attacks that would destroy a row of direct-sown seedlings.
• Collecting by torchlight: slugs and snails feed at night, and picking them off on mild, damp evenings in spring reduces numbers in a small garden.
• Watering in the morning: soil that has dried at the surface by nightfall is harder for slugs to cross than soil watered in the evening.
• Reducing shelter near vulnerable plants: slugs hide by day under pots, boards, low dense foliage and debris.
• Encouraging predators: a pond for frogs and toads, gaps in fences for hedgehogs, and log piles for ground beetles, as described under gardening for wildlife.
• Choosing plants they avoid: in gardens where hostas are shredded every year, replacing them is often the practical answer.

Once plants are established and growing strongly, most tolerate some grazing and protection can stop.