Slugs cost UK gardeners roughly £8 million annually in plant damage, according to Greenhouse Stores. These gastropods can destroy seedlings almost overnight, leaving irregular holes in flowers, leaves, stems, bulbs, potatoes, and tubers, along with a silvery slime trail.
Slugs remain active all year round, preferring cool, dark, and damp spots to prevent dehydration, and they often burrow into soil. Most active at night, they are a persistent nuisance for gardeners.
Garlic as a natural deterrent
Peer-reviewed research published in the Crop Protection journal by scientists at the University of Newcastle upon Tyne found that garlic acts as one of the most effective natural molluscicides, with the kitchen staple even capable of killing slug eggs in the soil. The pungent bulb serves as an environment-friendly pesticide while being extremely affordable, with a four-pack costing just 87p at major UK supermarkets like Tesco and Sainsbury’s — roughly 22p per bulb.
The reason garlic is so effective against slugs is because of the compound allicin, formed only when a clove of garlic is crushed, chopped, or chewed. Garlic is deeply off-putting to slugs, and strong enough concentrations can even be lethal to these pests. It is also harmless to humans, pets, birds, and other garden wildlife.
Making your own garlic spray
According to Sprouts of Bristol, the best way to keep slugs away is by regularly applying a garlic spray on your plants. The experts say: “A weekly application, plus an extra round after heavy rain, is key. It’s easy to make and safe for your plants.”
To make a basic garlic spray, take two whole garlic bulbs, no need to peel them, and two litres of water. Add the garlic bulbs and water to a saucepan and boil for around 15 minutes, until the garlic softens. Once softened, mash it to release the allicin, then strain out the garlic skins, leaving behind a cloudy liquid concentrate. Let the liquid cool before transferring it into a bottle.
Dilute two tablespoons of the concentrate in five litres of water in a spray bottle or watering can and apply to your plants and their leaves weekly. Store the concentrate in the fridge or a cool and dry place. Sprouts of Bristol recommend saturating both the leaves and the soil beneath your plants, applying the drench once a week from February to October, and reapplying after heavy rainfall.
Cold water method for potency
Experts at Chimney Sheep have one distinction to make, sharing: “Allicin is destroyed by heat. It starts degrading above about 60°C and by the time you've had a good boil on, it's pretty much gone. If you want a really potent brew, the secret is to make a cold water extraction instead. The cold water method keeps the allicin intact, which means the slugs sit up and pay attention to it. Simple, but important.”
To make a cold water garlic spray, take two whole bulbs of garlic, peel the cloves, and add them to a blender or food processor with 200ml of cold water. A garlic press also works — crush each clove individually and stir it into the water. Strain the mixture through a fine sieve or muslin cloth into a jar, ensuring all solid bits are removed to avoid clogging your spray bottle or watering can rose.
For a serious infestation, Chimney Sheep experts recommend using the solution neat on affected areas. Otherwise, dilute roughly two tablespoons of concentrate in a full five-litre watering can to treat a wider area. Store the cold garlic concentrate in the fridge or a cool, dry place, and make a fresh batch for every growing season.
