Commercial Products

Sea Shells: Often used as a decorative mulch around potted plants, broken shells are also sold as a slug barrier. These can be bought in tubs ready for direct application to your plants. A cheaper way to buy is to look out for sacks of shells at the garden center. The larger chains are not particularly interested in supplying shells by the sack but the smaller, family run businesses are usually happy to source them if they don't already have stock.

Shells work by making traction difficult for the mollusk, which is eventually covered in shell fragments. Incapacitated it dried out and dies.

Cockle shells are commonly available by the sack. If whole, the shells need to be broken into small fragments to be an effective barrier, too large and the relative weight of the shell will keep it on the ground as the slug moves over it. Breaking the whole shells is easily preformed by spreading a layer on a concrete path, laying a wide piece of wood or board over them an then walking on it. The weight of a person is enough to break them. This is easier if done in small batches. Care should be taken when breaking the shells as the edges can be very sharp, so thick gloves are useful when handling the broken shells.

If you decide to break them with the top of a heavy hammer then protective glasses should be worn as fragments can spin up from the pile.

The broken shells should be laid to a depth of about 4-5cm so that watering doesn't disturb it too much and reveal the soil or compost below. At the end of the season the shells can be reclaimed by pouring them into a sack for storage. A good percentage can be reclaimed this way as they do not tend to get washed down into the soil.

One of the potential pitfalls of this method of control is that sometimes shell fragments are carried back over the lip of a pot as the slug or snail makes a run for it (!) with pieces stuck to its foot. On decking this can be a nuisance, stepping on a broken sea shell in bare feet is not the best thing.

Egg Shells: Egg shells can be used in a similar way to sea shells if you have enough. They have the advantage in that they are easier to break and their light weight makes them stick to the slug or snail better than heavier shells. Another is that they are free if you eat eggs.

A potential problem is sourcing enough shells to cover even a small area to any depth. Flies may also be attracted to the wet inside surface if they are used straight from the kitchen and the smell prevents indoor drying.

Cocoa Shells: These are also more commonly used as a decorative mulch over borders and flower beds. They act as a physical barrier just like shells in that they stick to the slugs body making progress difficult. Cocoa shells also have another benefit in that they contain caffeine, recently discovered to be an effective control (see Caffeine in the Organic and Home-Grown section below).

A pitfall of this method, and any other that is based upon an organic mulch such as pine needles, is that as it rots down it provides just the environment that slugs like, damp and dark. It is a mulch after all and the traditional use is to help retain soil moisture. Applying fresh mulch will remedy this.

The shells also have quite a strong smell when fresh, a kind of bitter coffee smell. Some like it, some hate it. Make sure you're not in the latter group before you've spread it all over the garden, getting it back into the bag is going to be a problem.