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Why It Pays to Think Before You Sprinkle

Slugs are one of the few garden pests that can reduce a row of seedlings to stumps overnight, and it is tempting to reach for the blue pellets. It is worth pausing first. Those pellets, and the slugs that eat them, sit right at the heart of the garden food chain. Hedgehogs, thrushes, song thrushes especially, blackbirds, frogs, toads, slow worms and ground beetles all take slugs, and a poisoned slug is a poisoned meal.

The good news is that metaldehyde pellets were withdrawn from outdoor use in the UK in 2022, and methiocarb went years before that. What remains on many shelves is ferric phosphate, which is far less risky to mammals and birds but is still not harmless: it can affect earthworms, and earthworms are a hedgehog's staple. Used sparingly, in a bait station rather than broadcast, it can have a place as a last resort. Used as routine, it simply removes food from the wildlife you were hoping to encourage.

The realistic goal is not a slug-free garden. It is a garden where damage stays tolerable and the creatures that eat slugs carry on doing the work for you.

Know Which Slugs You Are Dealing With

Not every slug deserves a death sentence. The large black slug is mostly a recycler of decaying plant matter, and the leopard slug actively hunts other slugs. The culprits are smaller and less dramatic: the grey field slug, the garden slug and the keeled slug, which spend daylight hours tucked into soil cracks, under pots, behind wall bases and beneath low leaves.

That behaviour tells you where to aim your efforts. Surface baits and pellets miss most of the population, while anything that improves the soil, dries the surface or removes daytime shelter hits them where they live.

Barriers That Actually Hold

• Copper tape and copper rings around pots and raised beds work through a mild reaction with slug mucus. They need to be clean and unbroken, and they fail once the leaves of the plant bridge over the barrier.
• Sharp horticultural grit, crushed shell or wool pellets around seedlings create an uncomfortable crawl. Wool pellets also hold moisture and break down as a mild feed. Refresh after heavy rain.
• Keep barriers dry. Slugs will cross damp grit without much bother, so water in the morning and let the surface dry by evening.
• Lift plants off the ground. Pot feet, gravel trays, staked tomatoes, and removing the lowest leaves of brassicas all reduce the easy routes in.
• Tidy the edges. Long grass, damp cardboard and piles of old pots beside a veg patch are slug hotels. Move them well away from your beds.

Nematodes: The Quiet Biological Option

For beds, borders and containers, slug-parasitic nematodes are the most targeted treatment available. You water them onto moist soil in the evening, and the microscopic worms seek out slugs in the soil, where most of the damage is done. They are safe for pets, birds, hedgehogs, frogs and earthworms, and they leave no residue.

They need conditions to work. Soil temperature should be above about 5°C, so spring through early autumn is the window. Water the ground first, apply, then water again to wash the nematodes down into the soil, and keep the area moist for a fortnight. Expect the effect to last around six weeks, so a second application in late summer is often worthwhile. Buy fresh stock, store it as directed, and use it promptly rather than keeping it on a shelf until you remember.

Night Patrols and Simple Traps

Half an hour after dusk, especially after rain or an evening watering, is when the damage is done. A torch, a pair of gloves and a bucket will clear a surprising number, and a light with a red filter disturbs them less so they stay put while you work. Check stems, walls, the undersides of leaves and the rims of pots.

For daytime catching, lay damp cardboard, a plank or an upturned half grapefruit in the borders and check underneath each morning. It is a reliable way to gather slugs without touching bait. Beer traps are best avoided: they drown ground beetles and other useful predators, and the scent can draw hedgehogs in to drink.

Make the Garden Better for Predators

The most durable slug control is a garden full of things that eat slugs. A few simple changes make a real difference.

• Hedgehogs: leave a 13cm gap in fences so they can move between gardens, provide a hedgehog house, and check long grass before strimming.
• Thrushes and blackbirds: leaf litter to rummage in, a few berry-bearing shrubs, and a shallow bird bath kept topped up.
• Frogs, toads and slow worms: a log pile, a damp shady corner, and a pond with gently sloping edges.
• Ground beetles and centipedes: mulch, stone walls and a little undisturbed soil rather than digging every inch each autumn.
• Ducks: runner ducks on a smallholding will hoover up slugs, though they will also sample seedlings and need fox-proof housing at night.

Accept a little damage, and the balance tends to settle. A garden with hedgehogs, thrushes and frogs in it rarely has a slug problem it cannot live with.