Slug illustration

Non-toxic slug control in the garden

The following methods are non-chemical measures for slug control. All have been used with some degree of success and are offered here for you to try.

A slimy issue

It is not, however, possible to offer a guarantee of success, since the effectiveness of each method depends on the location and exactly how it is applied.

Look through the list and choose several techniques to try - don't rely on just one. A range of methods is much more likely to bring some success. 

Don't expect to get rid of all your slugs - that is just not a practical proposition. The aim is to protect plants while they are susceptible.

Garden friends

Though you may not think it, slugs have enemies too. They are eaten by frogs, toads, hedgehogs, centipedes, ground beetles, slow worms and fireflies, so make sure you don't use any chemical sprays which could harm them. Providing suitable habitat and food will encourage these beneficial creatures to live in your garden. 

However, do not be tempted to introduce predators like hedgehogs into areas where they don't naturally occur. This can change the natural balance on islands or in another environmentally sensitive areas. Hedgehogs eat the eggs and chicks of ground nesting birds and introducing them can create severe problems for native wildlife.

RSPB Rye Meads, family triathlon event, visitors bug hunting

Methods to try

Slug killers

Slug killers based on aluminium sulphate are not strictly organic, but they are environmentally friendly. They kill slugs and snails on contact with minimal risk to other wildlife or pets. Commercially available products using aluminium sulphate as active ingredient include Growing Success and Fertosan.

Protective barriers

Disposable plastic drinks bottles, with the bottoms cut off and the screw tops removed, make excellent individual protective cloches for young transplants. Check for the first few days after transplanting that a slug hasn't been trapped inside the bottle.

A slug and snail tape that creates a protective barrier is now on the market. Slugs are repelled by the small electric charge naturally contained in the copper face. Being self adhesive, it is easy to fix onto pots, seed trays, garden furniture, even onto sturdy plants.

SAS slug and snail repellent contains a natural yucca extract. When sprayed on the ground it forms a physical barrier which slugs and snails will not cross. As with many other repellents, it will withstand light rain, but will have to be renewed after a heavy downpour.

All sorts of materials such as lime, forest bark, crushed eggshells, wood ash, human hair and soot are said to make effective slug barriers, sprinkled on the ground around plants. The idea is that the barrier either dries out the slime that the slugs move on or that it irritates them so they will not cross it. Their effectiveness must inevitably be weather dependent but they may be worth trying, especially under cloches. Make a smooth seedbed type surface before applying a good layer of the material, a few inches wide.

Trapping

Slug traps are commercially available, and they can easily be made from empty plastic pots (eg large yoghurt pots) buried to half their depth in the soil and filled with milk and water, or beer. The slugs will climb up the sides, enter the tub and be killed.

These traps can be especially useful around newly planted out seedlings to help protect them until they grow away. Sometimes this sort of trap also catches the large, black ground beetles. Make sure the lip of the trap is at least 2cm above the soil surface. This should stop beetles getting in. As they eat slugs, they need to be encouraged, not killed.

Alternative feeding

A spring planted bed of lettuce is a real treat to the slugs as they may not have had a good meal recently.

It may be possible to keep transplanted plants safe for a while by offering an alternative food supply to slugs - such as lettuce or cabbage leaves spread between the plants. 

The slugs tend to collect under these leaves to feed and shelter, so examine them regularly and remove any that you find.

Another idea is to sow a sacrificial crop of something that slugs love, such as brassica or lettuce. Hoe this off while small and leave the hoeings in situ around the transplants.

Avoid susceptible plants

Gardeners too often want to grow things that aren't suited to their site. In the case of plants that are very susceptible to slugs this isn't really worth the effort. 

If, for example, the slugs get more out of your hostas each year than you do, the answer is to give up on the hostas and try something else. 

Alternatively, these plants can be grown in rough wooden tubs or terracotta pots, out of the reach of slugs. 

Baiting and hand picking

Slugs will inevitably collect in cool damp spots. This fact can be used to advantage as a method of reducing slug populations. A piece of damp cardboard held down with stone, or a piece of carpet, for example, is ideal; just lift it up at regular intervals and dispose of the slugs underneath it by dropping them into a pot of salty water.

If you cannot stand picking up slugs by hand, foreceps, tongs or thick rubber gloves can be very useful.

On damp evenings, and even on damp days, slugs will be out and about. This is the time to go out, with a torch if it is dark, armed with a salty water pot to pick up any slugs you find. Examine susceptible plants particularly. This is unlikely to reduce the slug populations in the long run, but it can save individual plants, which is most satisfying.

Winter digging

Autumn digging, leaving the soil rough and cloddy while the slugs are still active will allow those species that hibernate to move deep into the soil. If you must dig, do it in the winter while the soil is cold and the slugs are less active. This may also help to kill some slugs, and expose them to predators such as birds. While digging, look out for slug eggs in the soil. These are little clusters of colourless, round eggs, looking rather like small frogspawn or sago.

Biological control

This is a recent development in slug control. Microscopic nematodes occur naturally in the soil. They seek out and kill slugs by reproducing inside them. These nematodes are now being cultivated, and are available as biological control agent under the trademark Nemaslug. The nematodes are mixed into water and applied with a watering can to the area requiring protection. They remain active for up to six weeks. The nematodes are slug specific, and do not control snails.

Direct sown crops

Direct sown crops can be totally eaten off by slugs, especially in the early spring when top soil is cold and the seedlings are slow to emerge and grow away. Try to increase the rate of seedling emergence and growth by:

  • sowing later in the season, 
  • choosing the warmer, drier parts of the garden for early sowing (if there are any), 
  • pre-germinate the seed, 
  • improving the soil so it does not hinder germination. If the soil tends to set to a crust, cover the seed drill with some potting compost or sand mixed with the soil, 
  • if the soil has had a thick organic mulch over the winter remove it a few weeks before sowing to allow the soil to warm up. If mulches are used for growing crops, wait until the plants are well established before mulching. Mulches can harbour slugs, but they also provide shelter for slug predators, such as beetles.  

Transplanting 

If direct sowing always fails, the alternative is to raise transplants. They must again grow quickly to survive slug attack, so it is best to raise them in individual modules, so there is minimal check to growth when they are planted out. For the earliest plantings it is worth growing the plants even larger before transplanting - in individual plastic cups for example. For row crops such as peas, about 3ft lengths of plastic guttering can be used for sowing into. Whole sections of row can then be slid into place when the seedlings are well grown.

Potato slugs

The main attack on potato tubers happens in late summer and autumn, so lifting the crop by the end of August, at the latest, can help to reduce the damage. If lifting early reduces the crop too much choose early varieties and consider decreasing the spacing between plants to, say, 12 inches each way. This will reduce the size that each individual plant will reach, but it will also make them crop earlier - and because there are more plants than usual in the given space, the overall crop should not be reduced.

Slug pellets in garden border

Further information

Garden organic has kindly helped us to produce this factsheet. For further information on this or related subjects, please write to:

Garden organic 
Ryton Gardens 
Wolston Lane
Coventry 
CV8 3LG

Alternatively, find more information on the Garden organic website.

If you find dead birds in the garden, and suspect that they may have been poisoned by slug pellets they have picked up from somewhere, please report the incident to the Poison Helpline, tel: 0800 321 600. Make sure that you state that you suspect slug pellets as the cause of death.

For information on specific pesticides please contact:

Pesticide Action Network UK
The Brighthelm Centre  
North Road 
Brighton  
BN1 1YD

Tel: 01273 964230
Email: admin@pan-uk.org

Or visit the Pesticide action network UK website.

The RSPB encourages all gardeners to use non-chemical forms of slug control as much as possible. However, in the event of all non-chemical solutions being unsuitable or impractical, the RSPB welcomes and endorses the 'The Slug Pellet Code'. The code is as follows:

  • Use slug pellets wisely, and before use, always read the instructions on the pack.
  • It is essential that slug pellets are sprinkled thinly on the soil and around the plants being protected – not all plants are favoured by slugs and snails.
  • Individual pellets should be placed 10 – 15cm apart around the plant. Never pile them.  
  • Always secure the container and store safely out of reach of children and pets.
  • Always use and store slug pellets wisely.
  • Slug killers based on ferrous phosphate are becoming widely available through garden centres. They are safe for pets, crops and wildlife, and are the only ones allowed in organic gardening. 
  • Slug killers based on aluminium sulphate are not strictly organic, but they are environmentally friendly. They kill slugs and snails on contact with minimal risk to other wildlife or pets.
 Slug pellets in garden border with container