How can I prevent Slug and Snail damage?

Hostas in particular suffer greatly from attacks by slugs and snails; hemerocallis (daylilies) are less susceptible, but can still be damaged. Consequently many methods have been devised to prevent or minimise such damage. There is no one guaranteed method, but most have something to offer. They fall into several categories.

Garden Husbandry Slugs and snails love to shelter in untidy corners, and under stones, flowerpots, etc. Keep such hiding-places to a minimum; alternatively, check them regularly and destroy any slugs and snails you find there. They usually venture forth at night, so go round the garden with a torch, and pick off and kill any that you find; check the undersides of plants especially.

Natural Predators Thrushes love to eat snails, so encourage them by providing shelter, nesting places and food. Make sure also that there are hard flat surfaces on which the thrushes can break the snail shells. Discourage cats, as these will scare away the birds. Frogs and toads will eat slugs, and a pond (however small) will encourage these amphibians to take up residence. Hedgehogs also eat slugs, so encourage them by putting out food such as dog or cat food (but bear in mind that this might also attract dogs, cats and foxes). Hens, ducks and geese will eat slugs; unfortunately they sometimes eat everything else in the garden, and are noisy ? not ideal for the small urban garden!

Physical Deterrents Slugs and snails do not like crawling over rough, sharp surfaces, or over material that clings tenaciously to the slime on their foot. Such material as gravel, coarse sand, clinker, soot, chipped bark, crushed eggshells, hair-clippings from the barber’s and cocoa-shell mulch have all been recommended; they seem to work for some people but not for others. You can put sections of plastic bottles round young plants, and use longer strips of plastic or metal (copper and aluminium seem particularly effective), wire mesh or plywood around larger plants. Some people use thorny twigs such as pyracantha or berberis, or holly leaves, but these are potentially painful barriers. Putting hostas in pots also deters slugs and snails, especially if the pots are placed well away from places where the beasts congregate; it helps if you smear vaseline around the tops of the pots.

Chemical Attack Most commercial slug and snail killers are based on metaldehyde, which, contrary to popular belief, is not very toxic to other species; Gardening from Which? reported in August 1988 that a hedgehog would have to eat 2000 slugs poisoned with metaldehyde in one night to be killed. The blue colour of the pellets is also claimed to deter birds from eating them. If you are still worried, then there are slug-pellet containers that children and animals cannot reach into, or you can use a liquid formulation. Liquids penetrate to slugs underground, but they are shorterlasting than the pellets. A number of products contain aluminium sulphate, and these are usually claimed to be harmless to other species; however, aluminium sulphate does not seem to be quite so effective as metaldehyde. A third chemical, methiocarb, is, according to Gardening from Which? (August 1988), ” a more effective slug killer than metaldehyde, but it is also more poisonous to pets and wildlife “. Alcohol must be included in the list of chemicals; a saucer of beer placed in the garden will cause slugs to become intoxicated and drown. However, milk seems to work as well! There are one or two new products on the market which work by absorbing the molluscs’ slime; one such is Snail-Ban, an Australian product based on kaolinite and opal, and another is Molbar: yet another is Sluggo, which is claimed to work by stopping the molluscs from feeding, and is based on iron phosphate. Other chemicals that can be used are salt (sprinkled on the ground or directly on the slugs) ammonia (a 1 in 4 dilution of household ammonia sprayed on the plants or directly on the slugs), vinegar (diluted 1:1 and sprayed on) and potassium permanganate (1 teaspoonful per gallon, watered on). Some plant-based deterrents that are claimed to work are: a hot pepper spray (blend hot chilli peppers with water and a few drops of washing-up liquid), interplanting with prostrate rosemary or Artemesia absinthium, and spreading powdered ginger or short lengths of fresh-cut fennel or hyssop. Extracts of Phytolacca americana, garlic and ragwort are also believed to have a deterrent effect. Very recently, ground-up horse-chestnuts have been claimed to deter slugs effectively.

Nematodes Biological control is increasing in popularity, and one company (Defenders) markets nematodes which are claimed to be effective against slugs and young snails. They have to be ordered by post (you should be able to pick up an order form at garden centres) as they have a limited shelf-life. They are watered on, and should last for at least six weeks. They are expensive, but are reported to work well, especially in warm, moist weather.

Slug- and Snail-Resistant Hostas Hostas with thicker, more leathery leaves tend to suffer less slug and snail damage. One British hosta nursery’s catalogue lists 20 less susceptible hostas. Diana Grenfell in her book Hosta: The Flowering Foliage Plant (Batsford 1990) lists both vulnerable and resistant hostas, and Sandra Bond in her book Hostas (Ward Lock 1992) also has an extensive list of hostas least damaged by slugs and snails. There is even a hosta called Silvery Slugproof! 
Information supplied by the British Hosta And Hemerocalis Society

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