Keep slugs and snails out of the vegetable patch: step-by-step guide

We often say things like “that person is as slow as a snail” or “this situation is proceeding at a snail's pace”. Slowness and perseverance are traits commonly likened to slugs and snails, and these traits are much in evidence when the creatures slowly but surely invade your garden following a downpour, advancing out of nowhere through the grass and among your plants.

Although in everyday speech they are synonymous with similar things, snails and slugs shouldn’t be confused with each other. Both are terrestrial molluscs, but the former are recognisable by their spiral shell, and the latter by their unprotected, shell-less body: in fact, slugs have a reduced shell, hidden under the skin of the mantle behind their head.

Slugs and snails alike are the scourge of gardeners everywhere—albeit to differing degrees—due to the damage they cause to the vegetable patch and to the garden in general. Today we look at natural methods for controlling slugs organically, without upsetting the garden’s natural balance.

Let’s find out more about snails and slugs

Snails and slugs differ not only in terms of their appearance: the latter are the more voracious of these two molluscs, and so pose a more serious threat to your vegetables and ornamental plants. Even when you don't catch them in the act, you will know when slugs are at work. Obvious clues are the slime trails along the ground, on paving or on vegetation, and the holes made by their bites. They eat everything from shoots and young plants to leaves, flowers, vegetables and fruits. They also feed on vegetation below ground, such as tubers and bulbs. The damage they do is not limited to unsightly bites in lettuce leaves, strawberries and potatoes, but can ruin a whole crop of seedlings or transplanted vegetation, resulting in economic losses both to professional growers and to those who cultivate vegetables and fruit for their own consumption. Slugs are also capable of transmitting diseases between plants and contaminating them with pathogens that can infect humans and animals.

The word “mollusc” derives from the Latin word “mollusca”, meaning soft body. The body of slugs is primarily made up of water and protected from dehydration by a layer of mucus that also makes it easier for them to move. They are therefore mainly active at night, between sunset and sunrise, when there is less risk of their mucus drying out. During the day they become active in rainy or very humid weather, but when it is sunny and dry they remain holed up in damp and dark hiding places.

Keeping slugs out of the vegetable patch and garden with natural remedies

Getting rid of slugs permanently is nigh on impossible; consequently, as long as the damage they cause is only minimal and you are not faced with a slug infestation, it is perhaps better to accept that their presence is inevitable, at least in small numbers.

But however undesirable they might seem, they play a beneficial role in your garden’s ecosystem. In particular, they oxygenate the soil by burrowing, and they ingest and process organic matter (such as fallen leaves) which they then return to the soil, making it more fertile. For the same reason, in a compost bin they help to transform domestic and green waste into compost. In addition, slugs are a source of food for various wild and domestic animals. Last but not least, they are an indicator as to the health of your vegetable patch and garden: a slug infestation can be symptomatic of an unbalanced environment.

In broad terms, the strategies you can adopt against slugs are:

• Create barriers that protect plants.

• Keep slugs away from your vegetable patch and garden.

• Regularly remove any slugs you find.

Now let’s talk about methods of elimination: we suggest using only natural remedies against slugs. You can prevent slugs from reaching vegetation by creating barriers around individual plants, vegetable plots or flower beds, such as by installing specially designed, inverted L-shaped metal or plastic barriers in the soil, which form insurmountable obstacles for the slimy molluscs. Alternatively, you can liberally scatter the surrounding area with substances such as wood ash, sawdust, sand, lime, rock flour, coffee grounds, crushed eggshells or broken nut shells.

These mostly recycled materials stick to the body of slugs, irritating and sometimes injuring them, or even killing them through dehydration. Rain and humidity dissolve these treatments or make them ineffective, so you’ll need to routinely reapply them. Pay attention to possible “collateral damage”, for example ash and coffee alter the pH of the soil, by making it more alkaline in the case of ash, or acidifying it in the case of coffee: you can therefore mix or alternate them to cancel out their effects. We don’t recommend scattering table salt: it works very well against slugs, but in the long term it increases the salinity of the soil. To deter slugs you can also create green barriers consisting of repellent plants that slugs are averse to, such as garlic, lavender, nettle, rosemary, mustard or thyme.

Another way to keep slugs away from the vegetable patch is to capture them and transport them to where they cannot cause damage. This is feasible as long as the area is small: with a little patience you can pick them by hand at suitable times of day and when the weather is favourable. To maximise your catch you can lay shelter traps using cardboard, planks of wood, tiles, piles of straw and so on, which attract slugs by providing them with a damp, cool and dark place to shelter under.

To permanently eliminate slugs from the vegetable patch or garden, you can:

• Set beer traps around your vegetable patch, by burying glass jars up to the brim and filling them with beer: the smell will attract slugs, enticing them into the containers where they will end up drowning.

• Encourage the presence of natural predators such as hedgehogs, moles (at last, a good reason to tolerate them!), birds, lizards, toads and various insects: for example with an evergreen hedge you can create a perfect microhabitat for hedgehogs and other fauna. Even farmyard animals such as chickens are partial to slugs, and the shelter traps we described above will help you to gather a supply to feed them with. In addition, whenever you till the soil of your vegetable patch with a spade or a rotary tiller, you will unearth hidden slugs and the eggs they lay, leaving them at the mercy of predators and the sun.

• Use slug pellets containing ferric phosphate, which is an approved organic pesticide. It should be placed in small piles or distributed among the plants or, even better, scattered along the edge of the plots. Ferric phosphate is a selective pesticide, insofar as it affects only slugs and is safe for other animals; what’s more, it enriches the soil with nutrients that benefit plants.

Speaking of slug killer: avoid using it as a quick fix, but only as a last resort, such as when there is an actual slug infestation and other natural remedies have proven insufficient. In any case, we don’t recommend metaldehyde-based products, because metaldehyde is an active ingredient that leaves toxic residues in the soil and is very dangerous for dogs, cats and other animals (such as hedgehogs). If you do decide to use it, place it in slug bait stations buried around the perimeter of the area that you want to protect. This will help to avoid using an excessive amount of slug killer and will prevent it from coming into contact with the soil.

What is the best way to keep slugs away from the vegetable patch and garden? It’s difficult to give a definitive answer: it is worth experimenting and adopting an integrated approach by combining multiple tactics, just like we suggested for ridding your garden of mosquitoes.

How to prevent a slug infestation

By keeping your vegetable patch, garden and surrounding areas tidy—for example by cutting the grass with a brushcutter, lawnmower or garden tractor—you prevent the creation of optimal conditions for the proliferation of slugs. On the other hand, an excessively tidy garden isn’t a very a hospitable environment for predators of slugs.

Biodiversity ensures a balanced, self-regulating habitat, thanks also to the dynamics that are established between prey and predators. A garden rich in biodiversity offers slugs alternative food sources to your vegetables and plants, while also exposing them to natural predators. Biodiversity encompasses plants, animals (including slugs) and microorganisms: we talked about this in this article on how to design a sustainable garden.

As everyone know, slugs love moisture, so it is advisable to avoid the accumulation of standing water on your vegetable patch and garden. For example, opt for drip irrigation rather than relying on rainfall or hosepipes to water your plants. It’s widely accepted that mulching provides various benefits to soil and plants but, at the same time, it can encourage the presence of slugs.

Standing water is more likely to occur if the soil is clayey: in our corresponding article you will find suggestions for keeping the soil of your vegetable patch soft and preventing it from recompacting easily. In an emergency you can drain puddles with a water pump, but to solve the root problem it may be necessary to create a drainage channel or infiltration system such as a dispersion trench or dry well.

Besides slugs, moles and mosquitoes, among the least welcome guests in the garden are ants and various plant parasites. Instead of resorting to synthetic products, you can protect your vegetation by applying natural treatments with a sprayer pump or mistblower.