Natural Ways to Deter Slugs and Snails

There is something deeply unfair about slugs and snails. You spend weeks raising sturdy little seedlings, harden them off, tuck them into freshly prepared ground, and by morning half of them have vanished and the rest look like lace. Every allotmenteer in Britain knows the feeling. The good news is that you do not need to reach for a blue pellet to win the battle. A combination of good housekeeping, a few well-placed barriers, and a willingness to wander out with a torch after rain will keep losses to a manageable level.

Know What You Are Dealing With

Slugs and snails are not identical problems. Snails mostly work above ground, climbing stems, brassicas and fruit bushes, and they leave the tell-tale silver trails. Slugs do their worst at ground level, and the small keeled slugs that spend almost all their time below the soil surface are the ones that hollow out your potatoes and carrots.

Both are nocturnal and both adore damp conditions. A wet evening after a dry spell brings them out in force, and a single grey field slug can do a surprising amount of damage between dusk and dawn. They lay clusters of translucent eggs in soil crevices and under debris, which is why clearing rubbish from your plot does more good than any spray. Understanding the pattern matters: control the moisture and the hiding places and you control the population.

Remove the Places They Hide

This is the least glamorous job on the plot and the most effective. Slugs and snails need shelter during the day, and an untidy allotment is a five-star hotel.

• Clear planks, old pots, bricks, sacks and sheets of plastic that have been lying about for months.
• Keep grass paths mown short, and strim the edges of beds where vegetation grows tall and damp.
• Tidy the base of the compost heap and turn it occasionally so it does not become a nursery.
• Thin out overcrowded rows so air moves through and the soil surface dries.
• Lift the lower leaves of courgettes, brassicas and pumpkins clear of the soil, and stake anything that flops.
• Water in the morning rather than the evening, so the surface has time to dry before nightfall.

Once a week, walk the plot and flip over anything you cannot move. You will usually find a cluster of slugs underneath, ready to be dealt with.

Barriers That Genuinely Work

Copper is the most reliable physical barrier available to the kitchen gardener. Slugs and snails react to copper with a mild irritation, and they will not cross a continuous strip of it. Use copper tape around the rims of raised beds, pots and cold frames, or copper mesh as a collar sunk a few centimetres into the soil. The crucial detail is continuity: if a single leaf drapes over the tape and touches the ground, the barrier is finished and they will find it.

Other barriers are worth trying, particularly around individual plants. Crushed eggshells, sharp horticultural grit and wood ash all create an uncomfortable surface, but they only work while dry, so renew them after rain. A ring of bran or a sunk beer trap will lure them away from your seedlings; set the rim of a jar two centimetres above soil level so ground beetles do not fall in, and empty it every couple of days. For the underground keeled slugs, a nematode drench applied in spring while the soil is warm and moist is a worthwhile investment.

Recruit Some Allies

The best long-term strategy is to make your plot attractive to things that eat slugs and snails for a living. Frogs, toads, slow worms, hedgehogs, ground beetles, centipedes and thrushes will all do the work for you if you give them somewhere to live.

• Sink a small pond, or even a deep washing-up bowl with a ramp of stones, to bring in frogs and toads.
• Build a log pile or a leaf mound in a quiet corner for beetles and slow worms.
• Leave a rough, wild patch at the boundary rather than keeping every inch pristine.
• Encourage birds with dense hedging, a berry-bearing shrub or two, and a shallow water dish.
• Never use metaldehyde pellets. Hedgehogs, birds and pets are all at risk, and the slugs that survive simply come back.

If your site allows poultry, a few ducks will clear a plot of slugs with alarming efficiency, though they will also eat your salad leaves, so keep them contained.

Plant and Plant Out More Cleverly

Strong seedlings survive attacks that destroy weak ones, so raise as much as you can in modules and plant out sturdy, well-rooted specimens rather than sowing everything directly. Avoid planting out just before a wet spell if you can help it, and keep vulnerable crops under fleece or cloches for their first fortnight.

Sacrificial planting works well on an allotment. A row of cheap lettuce or a few marigolds at the edge of a bed will draw attention away from your prized crops, and you can clear the decoys, slugs and all, every few mornings. Densely planted, strongly scented herbs such as thyme, rosemary and lavender may not repel anything, but they do provide cover for the beetles that hunt slugs, which amounts to the same thing.

The Nightly Check After Rain

If you take one habit from this article, make it this one. An hour or so after dark, especially after rain or during a damp drizzle, take a torch and walk your plot. Look along the edges of beds, under the lower leaves of brassicas, around the drip line of cloches, and anywhere you have spread mulch. A head torch keeps both hands free for the bucket.

Drop what you find into a bucket of soapy water, or carry them to a hedgerow well away from the plot if you prefer. Ten focused minutes, three or four nights a week through spring and early autumn, will prevent far more damage than any product you can buy. Do a patrol a week before you intend to sow or plant out and you will start with a much lower population.

Combine the evening patrol with a morning check of your traps and you will soon notice the difference. Fewer nibbled leaves, stronger plants, and a plot that supports frogs, birds and beetles rather than working against them.