Hanging Hostas is one way of deterring slugs and snails; The Hanging Hosta Garden, Lindford, Hampshire ; © J. Colley

Hostas

Traditionally we celebrate St. Valentine's Day by giving cards and presents to our loved ones. But we should also remember to love our hostas on St Valentine's Day. This is the day to start using slug deterrents or other means of disposing of these pestilential molluscs. Acting then will ensure that one's hostas produce foliage as sumptuous as that of the accompanying image of the pristine leaves of Hosta 'Great Expectations'.

The reason for this is that the slug that does most damage early in the season is the keeled slug, Milax spp., which lives underground and out of sight but becomes active at about this time of year. In late winter/early spring the keeled slug migrates towards the surface of the soil where it can do untold damage to emerging shoots and leaves. The damage done at this time of year may make the hostas unsightly for the rest of the year. Out of sight should not be out of mind for hosta gardeners!

There are a variety of ways of controling slugs and snails. Some only work on contact as they are applied, others remain active for longer and others still purely function as deterrents.

Hand Picking

Arguably the most satisfying and greenest method of slug control is to pick the pests off the leaves yourself and destroy them as you see fit. This is best done just after dusk as the molluscs start to emerge from their hiding places to feast on your precious plants.

Slug Pellets

Pellets have proved to be a cheap, popular and effective control for slugs. However, the usual blue pellets contain metaldehyde, which some people are uncomfortable using as it can be harmful to pets and wildilfe. An alternative to this, which is being marketed as organic and safer around pets, is based on iron (ferric) phosphate. It works by the pellet swelling up inside the slug, preventing it from eating, thereby killing it. We would recommend that prospective purchasers do their on research on the dangers of all slug pellets, include those containing iron phosphate, being buying them.

Barriers

If hostas are grown in pots, then grease or vaseline can be applied or copper bands fixed around the sides of the pot.  
There are a couple of theories as to why copper bands work reasonably well as a deterrent; one is that copper is poisonous to slugs and the other that a small electric current is generated as the slug slides over the copper, in a similar way to the functinoing of a battery. The science is less than conclusive for both of these theories, but the method itself seems to work. 
For any plants grown in the ground, grit, sheeps wool or even coffee grounds are said to be effective, although in my experience these deterrents have mixed results. 

Garlic

Garlic, which has ben used for centuries in the battle against slugs and snails, works as both a deterrent and a contact killer. Although it's not known exactly why the chemical iin garlic is so potent for the molluscs, it will kill them and any of their eggs within hours of application. Regular application is needed though (once every week to ten days), usually in the form of a spray, to keep the slugs and snails under control throughout the season. Garlic sprays are available commercially. Alternatively, they can be made at home by simply crushing and boiling 2 cloves of garlic in water, straining and diluting with more water to make up to 25l of solution.

Ammonia

Household ammonia can be used as an effective contact killer for slugs and snails. It should be diluted to about a 10% solution in water and sprayed onto the leaves. Being an active ingredient if fertilizer, ammonia is harmless to plants in this concentration - in fact, it's probably benefitial .Please remeber though, it acts only on contact; it doesn't stay effective for long in solution in the soil.

Some people have reported that chicken manure fertilizer, which contains ammonia, has been an effective deterrent for slugs and snails. It's not clear why this should be the case - possibly the texture of the granules, or the release of gaseous ammonia from the manure. The BHHS will be conducting trials on this product next season.

Daylilies

Slugs and snails are rarely a significant problem. In prolonged periods of drought, slugs and snails may be tempted by the leaves of seedlings and new divisions.

General

The British Hosta and Hemerocallis Society suggests you follow the latest advice from the RHS on controlling slugs and controlling snails.
Hosta 'Great Expectations' © June Colley
Hosta 'Goldbrook'