The truth about slug control: separating fact from fiction

It’s also worth remembering that not all slugs are a pest. Many slugs are useful in the garden, such as the Leopard slug, which doesn’t eat healthy plants. It feeds on fungi and dead plants.

Discover six of the most common 'hacks' for dealing with slugs and snails and whether they actually work. Plus, we share expert advice for tried-and-tested solutions to slug and snail problems.

6 common slug and snail deterrent ‘hacks’

1. Coffee grounds

Coffee grounds are said to act as a deterrent to slugs and snails when used as a barrier around plants. The theory is that slug and snails don’t like the smell of coffee grounds or travelling over a gritty surface. Some studies have shown that a caffeine solution sprayed on to plants repels slugs but it’s not good for some plants, such as tomatoes, and can prevent the germination of seedlings.

Expert’s opinion
“Caffeine can have a negative effect on plant growth. A study published in 2023 found that unless coffee grounds had been composted for less than seven months they were bad for plants. The caffeine in coffee can also be toxic to lots of organisms such as frogs so this method isn’t one I’d recommend using in the garden,” Hayley says.

2. Eggshells

Eggshells, like other physical barriers, are supposed to deter slugs and snails due to their texture – snails and slugs don’t like crawling over the sharp eggshells. Other barriers include wool pellets and horticultural grit. Anecdotally, this is said to work but recent studies on physical barriers, conducted by the RHS showed no difference between lettuces planted with a barrier of eggshells around them, and those without a barrier.

Expert’s opinion
“Slug and snails don’t feel eggshells and similar barriers like gravel, which are sharp, like we do. They have mucus on their foot, which helps lubricate their way along. So if there’s something tasty on the other side they will produce thicker mucus and cross over without any impediment.”

3. Greasy barrier

Instead of using a gritty textured barrier, try applying a greasy one like Vaseline or WD40, to prevent slugs and snails getting over the top of pots. The evidence for this is mainly anecdotal.

Expert’s opinion
“This isn’t one I’ve seen studied but it could have potential. If slugs and snails can’t adhere to the surface of a pot, they wouldn’t be able to cross. It’s worth thinking about how often you’d have to apply it.”

4. Beer traps

Fill a container with beer and sink it into the soil, near the edge of a border with vulnerable plants. Leave the top of the trap sticking 1cm above the soil to prevent other creatures falling in. Slugs and snails are attracted to the smell of the fermented ingredients in beer and fall in. A small citizen science experiment run by Garden Organic found that when two types of trap were put down – one containing water and one containing beer, the beer traps caught significantly more slugs. But yeast mixed with water is also attractive to slugs.

Expert’s opinion
“Studies on beer traps often measure success by the number of slugs caught, but they haven’t measured whether the plants nearby are less eaten. There’s no evidence to show whether the traps are working to stop slugs eating plants. You may also catch the good slugs as well as the [ones that eat your plants].”

5. Copper tape or rings

Gardeners use copper rings in the ground, placed around plants like hostas, and stick copper tape around the rim of pots to stop slugs and snails climbing in and demolishing seedlings. Bury the copper rings deeply to prevent slugs getting access to plants from underneath the ring. A trial carried out by the RHS found copper tape on pots to be ineffective, but many gardeners use this method. According to Dr Jones, copper is a deterrent, because the chemical salts taste bad or toxic to slugs and snails. They taste through their feet and their tentacles.

Expert’s opinion
“Copper does have good evidence for being a deterrent, but it depends on the format. Slugs can go underneath a collar that’s resting on the soil and many copper collars aren’t that deep. Copper tape should work around pots, but I have seen slugs crawling over it without hesitating. This might be because some copper products that are sold are laminated so the slugs or snails aren’t coming into contact with the copper. Just make sure the product you buy is real copper. And look at thickness – bigger slugs might be able to get over a thin strip.

Using copper on pots is safer as the food is further away so slugs will be less motivated to climb up a dry pot and then over a copper barrier. The risk on the ground is that they will put up with some discomfort to get to the plant.”

6. Garlic drench

Garlic releases allicin when it is chopped or crushed, a compound that is said to repel and even kill slugs and snails. One study carried out by Newcastle University found that garlic solution killed slug eggs. A garlic drench is made by boiling garlic bulbs in a couple of litres of water. The resulting liquid is diluted and used as a spray for plants, usually in the evening.

Expert’s opinion

“This is a pesticide rather than a deterrent. We don’t know what effect it might have on other garden [creatures] as it can kill slugs. [I wouldn’t advise making your own pesticides at home].”

Tried-and-tested ways to tackle slugs and snails

There are some tried-and-tested ways to tackle slugs and snails. Some slugs can be helpful in the garden, feeding on decomposing material in compost heaps. If they are munching on your lettuces and seedlings though, there are a few ways to keep populations under control:

• Water in the morning – “If you water in the morning rather than the evening, it has a noticeable effect on slug activity. Watering in the evening creates a damp film and ideal conditions for them to travel. In one study, watering in the morning was as effective as one application of slug pellets,” says Hayley.
• Lay mulch – using a dry mulch that covers the surface of the soil, rather than a barrier around plants can reduce slug damage. At RHS Harlow Carr it reduced slug damage by 20 per cent. A straw-based mulch works well and mulches have the added benefit of being good for plant health.
• Encourage predators – making your garden wildlife friendly can help to keep down herbivores. Common predators of slugs and snails include birds, frogs and hedgehogs. Keep an eye out for clusters of slug eggs and leave them exposed for birds to feed on.
• Pick off snails and slugs – going out at night and picking slugs and snails off your plants by hand is an effective way to keep populations down. Move them to your compost heap or at least 20m away, as they can find their way back from a shorter distance
• Prioritise protection of target plants – if you have a big problem with slugs and snails it can be difficult to put protective solutions everywhere so concentrate on the plants they like most. These include seedlings, veg plants like lettuce, fruit such as strawberries and hostas.
• Choose different plants – if slugs and snails are a severe problem in your garden consider using different plants. Swap hostas for another attractive foliage plant such as Alchemilla mollis, which slugs don’t like. Choose potato varieties that are less likely to be eaten and protect seedlings indoors until they are strong enough to withstand an attack
• Use a biological control – there are nematodes available that specifically kill slugs. Follow directions carefully as the soil needs to be a certain temperature for the application to work. You may need to apply several times throughout the growing season.