David Kuchta, Ph.D. has 10 years of experience in gardening and has read widely in environmental history and the energy transition. An environmental activist since the 1970s, he is also a historian, author, gardener, and educator. 

Slugs and snails can be a mixed blessing in your garden. Slugs are almost exclusively a nuisance, while snails can have some benefits. Generally speaking, however, the drawbacks of each outweigh the benefits, so keeping them under control is key to maintaining a healthy garden.

Slugs and snails are opportunistic feeders, eating whatever is available. Slugs eat all types of vegetation, from roots to shoots—which makes them more destructive than snails. But slugs can also eat small invertebrates, keeping them from overpopulating a garden. The presence of a small number of slugs isn't necessarily a bad thing.

Unlike slugs, snails are primarily decomposers that feed on dead leaves and flowers, speeding up the recycling of plant nutrients. Their feces fertilizes the soil much more quickly than bacteria breaks down plant material. Earthworms decompose plant matter at about the same rate as snails do, and are far less detrimental in the garden.

While it is not their primary food, snails will eat bug eggs when there is little other food available. They will also feed on the eggs of slugs and other snails, allowing them to act as a natural pest control in a balanced ecosystem. However, they will eat the eggs of beneficial insects as well as those of pests.

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When slugs and snails hide underground during the heat of summer, they create small burrows that can aerate the soil. This can be beneficial both to your garden as well as to your compost pile, since air is necessary for decomposition.

When snails die, the decomposition of their shells slowly adds calcium to the soil. But generally, most soil contains a suitable amount of calcium, so the small amount of additional calcium makes little difference to your soil. And slugs, of course, carry no shells on their backs.

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Both snails and slugs feed at night, making them harder to detect and control. Snails prefer to eat decaying materials, and only eat living vegetation when it's the only food available. By contrast, slugs cause far more damage in a garden than snails. While some slug species eat fungi and algae, or feed only on decaying material, slugs found in gardens will eat live plant leaves, fruits, vegetables, grass, fungi, and even bulbs and soft roots.

There are numerous ways to get rid of snails and slugs naturally. You can, for example, reduce the dark and wet places where snails and slugs like to hide. Rather than watering your garden with a hose or sprinkler that sprays whole areas indiscriminately, use a soaker hose or other form of drip irrigation to only water the plants that need it, rather than watering leaf piles or wood piles that attract snails and slugs.

You can also remove snails and slugs individually. Since both are nighttime feeders, you'll want to go out after dark, don some garden gloves, and remove snails or slugs from your plants. You can relocate them to your compost bin if you have one. This will aid in the decomposition of your yard and food waste.

But the most effective control is a systemic one. In moderate numbers, the presence of snails and slugs can be a sign of a healthy garden. Native slugs and snails play a role in any natural ecosystem; they are only a problem if there are no natural predators to feed on them.

Monocultures are more frequently the target of infestations of all sorts, so creating a garden that is as close to a balanced ecosystem is key to living with slugs and snails—even invasive ones. A permaculture garden with a variety of plant species will attract species that feed on snails and slugs and keep them in check. Birds are natural predators of snails and slugs, as are ground beetles, garter snakes, turtles, lizards, frogs, and toads. Attract songbirds with a native tree for them to perch on, a bird feeder, and a bird bath. Create a small pond to attract amphibians and reptiles. Predatory nematodes can also be used to control the slug population.

A diverse garden can also include plants that snails and dislike, which will persuade them from overrunning your garden. While slugs and snails prefer brassicas and greens, they stay clear of highly scented plants like geraniums or rosemary. Inter-planting vegetables, herbs, with strong-smelling perennials can repel slugs and snails. Mimic the biodiversity of nature and you are more likely to keep slugs and snails in check.

A common assumption is that the sharp edges of eggshells or gravel act as deterrents to slugs and snails, but studies show that the thick slime that the animals produce acts as a protective shield, allowing them to slide right over sharp objects. If you have the stomach for it, you can find videos on YouTube of slugs and snails crawling over knife blades, razor blades, and other sharp edges.

Most commercially sold slug pellets contain metaldehyde, which can harm wildlife and is banned in the United Kingdom. Alternative pellets contain ferric phosphate, a poison that can also kill beneficial earthworms and even pets if it is consumed in large quantities. Slug pellets can also kill their slugs' predators.

Jones, Hayley, et al. "Gastropod Barriers." Royal Horticultural Society, 2018.

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