Wildlife Gardening - Natural Slug Control
Created | Updated Sep 10, 2013
Introduction | Mammals and Birds | Woodland Habitat
Insects, Amphibians and Reptiles | Wildflower Meadow | Water Habitat
Natural Slug Control | Natural Weed Control | The Winter Border
Although most people think of slugs as pests, they are as necessary as the more attractive visitors to our gardens. They help to break down decaying plant matter, disperse seeds and spore and provide a very rich compost-like waste which feeds the garden. They also provide food for more welcome visitors, such as birds. While the removal of debris is not as valuable in our cultivated gardens as it in the wild, this can be used in the fight to save our prize vegetables, and vulnerable seedlings and young plants.
Many gardening articles recommend keeping gardens scrupulously clean of debris to discourage slugs. As the wildlife gardener is encouraged to leave the garden in as natural a state as possible, some of the recommendations in this entry may contradict other advice. This entry does not discuss how to kill slugs, only how to gently discourage them from eating your prize plants, although it will discuss ways of encouraging other creatures that will hunt down and eat them. It's like the Serengeti in your garden...
Work With Them, Not Against Them
Slugs don't like tough leaves, they like tender morsels, which is why they always seem to eat the young plants first. They like leaves that are beginning to wilt, so if you do some weeding, leave the weeds around for a few days as the slugs will eat those first. Use local mulch as much as you can - slugs love wet leaf mulch, and are far happier staying in the damp and eating dead leaves than venturing into the open spaces in your flower beds.
Although it is possible that this will encourage more slugs into your garden, if you have a healthy population of other creatures that eat slugs, you will be providing them with food, and there will be a balance.
Plant lots of things that are native to your area; they will be used to the local wildlife, and will have developed ways to defend themselves from slugs. As slugs like the damp, they will be more numerous on top of the soil after it has rained, or when you have watered the garden.
Because slugs have to produce mucus (slime) to move, they prefer not to move over anything dry, dusty, or scratchy. They need to produce so much slime to travel over gravel, sand, ash, or lime that they can exhaust themselves in dry weather, and they die. This is not a foolproof method, as they have been seen to travel over beds of broken eggshells to find a meal. However, it will act as a deterrent, especially when combined with some of the other tips in this section. They will not waste energy in this way, when there is a pile of wilting leaves that they can easily reach.
The toad is the slug's worst enemy, although there are other things that eat slugs and snails. Ground beetles, slow-worms and frogs, even centipedes will eat them, as well as birds. Put in a wildlife pond if you can, or simply provide a container with water - as long as the toads have access, they will come, bringing frogs with them. It will also encourage birds to visit your garden more often.
Ground beetles share the same habitat as slugs; moist areas that are protected from the sun during the day. Provide stone slabs, pieces of wood, and other moist areas for them to shelter under. This will also encourage hedgehogs, which eat slugs.
To make it easy for birds to eat them, place citrus peel or melon rinds around the garden in the evening. The slugs will be attracted by any seeds remaining, and will stay under as daylight comes. Turn the peel or rind over in the morning to display the sheltering slugs to birds. Birds will also eat the eggs, so raking the garden can expose them. The majority hatch in spring, although eggs are laid all year round.
Phasmarhabditis Hermaphrodita is a naturally occurring nematode in the UK, and it eats slugs. Nematodes are microscopic worms that feed on insects, plants and animals, and are extremely numerous - one handful of earth will contain thousands of them. This species kills by entering the body of the slug while it is underground, to begin feeding and release bacteria which is fatal to the slugs. Being hermaphroditic, they reproduce internally. When the slug dies, the nematodes are released to find another victim. They do not harm other organisms.
Packets of this species of nematodes can be bought to add to damp soil, and they remain active for around six weeks. Slugs have been seen to avoid earth treated with nematodes, so they are ideal for natural slug control. Add them to the area where you are growing your most vulnerable plants and they will be well-protected without the need to treat your entire garden.
The Barrier Method
Other ways of preventing slug damage include ways of physically keeping them away from plants.
The Natural Barrier
Seaweed is a natural repellent to slugs, as it is salty. Pack it around 3-4 inches around the plants that you want to protect, making sure it doesn't touch them. The slugs will stay away, as the seaweed will dehydrate them. When it is dry, seaweed becomes very rough, so will still deter the slugs.
When slugs make contact with copper, a toxic reaction occurs between the copper and the slime creating an electric current, and they get an electric shock which repels them. The benefits are that it works wet or dry, is very effective, and doesn't kill the slug. The copper must be at least 2" wide, preferably 3" to be a real deterrent. It can be bought as adhesive tape, or strips. Bury it in the ground a couple of inches to prevent them crawling under it, and bend the strips so the edge sticks out at an angle. This will help to put off the more determined slugs who are willing to put up with the discomfort. Copper can lose strength over time, so go over it with sandpaper from time to time.
The drawbacks are that it can be expensive, so use it sparingly, perhaps on containers, rather than the borders. The edges can be sharp, so keep away from where children play. If the plants overhang the copper strips, and touch other plants or the ground, this will act as a bridge, and slugs will climb straight over. Make sure that there are no slugs inside the area you are protecting, otherwise you are trapping them in with your plants.
Gardening tools are also available in copper. These have been said to have a beneficial effect on keeping slugs away from plants.
Home Made Fortifications
Young plants can be protected when they are planted with a few household objects. Take a plastic drink bottle, cut off the top and bottom to make a tube. Cut one end into nasty spikes and bend most outwards. Spray the top and spikes with WD40, as this is a lubricant they will not be able to get a grip, and push at least 2" into the ground. Cover the soil around the base of the plant inside the tube with sharp gravel or pine-needles.
For established plants, make two tubes as above, slit each one up the side, and put round plant together with slits facing in opposite directions.
There are a few other suggestions that may work. The author has not tested these, but sometimes anything is worth a try.
If you know a friendly hairdresser, you can try putting the sweepings from the floor around your plants. The cut ends are sharp, and may put the slugs off. The hair will decompose and benefit the soil, although in windy weather it might not be pleasant.
If you are growing plants on benches, try wrapping bare copper wire around the legs. This should deter slugs from climbing. This can be used on anything you can wrap it around.
Ducks will make a meal of as many slugs as they can find. However, they come with their own problems. Caution and lots of research is recommended before ducks are brought into the cultivated garden. There is lots of information about keeping ducks at the British Waterfowl Association, and some things to think about before you impulse buy a duck as a present for a gardener you might think will like one.
'Natural' Slug Control Not Recommended
There are some ways of killing and repelling slugs that are not recommended for the wildlife gardener. We have included the better-known methods here, with reasons for not recommending them.
Diatomaceous earth is made up of the very jagged, fossilised remains of microscopic creatures from the sea. The microscopically-fine edges are as sharp as broken glass and lacerate the skin of slugs. This causes them to dehydrate and die. Non-toxic to humans and large animals, it is also sold as an insecticide, as it strips the exo-skeleton from insects, and so can kill beneficial insects as well. It is applied as a fine powder, and will need to be reapplied every time it rains. Time-consuming and costly, there are better ways to protect your plants from slug attacks.
Caffeine kills or deters slugs, depending on the strength of the brew. A 1-2% solution will kill them, and a 0.01% solution will repel them. Instant coffee is around 0.05%, with brewed coffee being stronger, so throwing a cup of coffee over the soil will not help, especially as it can also kill beneficial insects. Strong solutions can affect some plants, causing leaves to turn yellow or display brown stains. If coffee grounds are placed directly on the ground, they can go mouldy if not spread thinly enough, and is not the best way to get the caffeine into the slugs. Spraying the plant with a 'cup' of coffee would work as a deterrent, but it would need to be constantly reapplied to put the slugs off their tea, and is likely to only work on small and young slugs.
While it can be very satisfying to dissolve slugs with salt, it's not a very nice way to die and is unpleasant to clear up. Using salt as a barrier around plants should be avoided, as it is bad for the soil.
'Slug pubs' are often proclaimed as a wonderful way of getting rid of slugs. Some type of beer or ale is poured into a vessel, which is dug into the soil, occasionally left with some form of 'shelter' over the top, and then left for the slugs to fall into and drown. The reason this is not recommended is because it's a terrible waste of beer. Although people who have tried it swear by a particular brand or type, it's actually the yeast that the slugs are attracted to.
There are other reasons for not recommending this method. Other insects and animals can fall in and drown, many of which are considered very beneficial to the garden. Ground beetles are a very common casualty, and they are a slug predator, so they should be kept safe. It also involves cleaning out the dead every day, and replenishing the beer. There are many ways to keep the slug population down without resorting to indiscriminate killing.