Slugs and Snails

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.

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
Preparation of Garlic Juice (Hosta Handbook 2018 by Colley-Baker)
   The best and most cost-effective method of application is by spraying the leaves and stems of the plant. We use a pump spray bottle. Ian Scroggy has formulated a recipe which was circulated to the Society some years ago.
 
   Take two whole bulbs of garlic, place in a plastic bag and then crush to a pulp using a rolling pin or hammer. Empty the pulp into a pan and add a litre of water. Bring to the boil and simmer for five minutes. Strain the milky juice into a jug and squeeze the pulp to remove all the garlic liquid from it.
 
   Store this concentrated garlic juice in an airtight dark bottle or plastic container in the fridge and label it ‘Garlic’. It might be useful to put the bottle inside a plastic bag or two so no odour escapes to contaminate the contents of the fridge.
 
   An alternative to garlic bulbs is dried garlic granules sold by pet shops as a horse feed to prevent insect bites. This is in fact more cost effective. Boil half a cupful in a litre of water to produces a strong concentrated juice.
 
 Add two tablespoons of garlic juice per litre of water in your watering can or spray bottle and apply to the hosta leaves and stems when the plant is not in bright sunlight. 
 
   Apply the spray every two weeks. You may need to apply again after rain as this will wash the garlic into the soil. It is beneficial also to spray other plants near to the hostas as slugs and snails often hide in other plants during the day. While the garlic juice has an odour, the garden will not smell strongly of garlic because it is diluted in the water. The mild odour will only linger for a few hours, but the spray is sufficient to repel the slugs and snails. Ian Scroggy adds mint to the solution to repel other insect pests.
 
*New research from the University of Plymouth suggests it may be the smells produced by young seedlings that attract the molluscs. ... In other words, researchers compared the snails' selection of plants based on their taste (CSDMs) and on their smell (VOCs).



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'