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Slugs & snails

Helping plants survive slug and snail attack

Angelica gigas (biennial) with Helianthus behind
Angelica gigas with unwanted guest

My garden always endures snail and slug damage – 2015 and 2016 were exceptionally bad, with so-called ‘sleepless slugs’.

They’re soft-bodied molluscs, snails having the hard shell, the two most populous being the common garden snail and banded snails, which are smaller with yellow, white and brown markings.

Slugs vary in size from the grey field slug, no more than 5cm long, to the large black slug (which can also be orange/brown or buff), which can be 12cm long.

All snails and most slugs live in or on the soil surface, but keeled slugs live and feed mostly in the root zone – the potato pests.

Active after dark

Both are most active after dark or in wet weather, and their slime trails and holes in plant tissue, made by their rasping tongues, will tell you of their presence. They’re surprisingly good climbers.

Snails are less common than slugs in acid soil areas and, unlike slugs, remain dormant in winter, huddling together in protected places.

Hosta snails
Hosta after a severe snail attack

Reproduction happens mainly in autumn and spring when clusters of spherical, yellowish-white eggs can be found under logs, stones, and pots.

Common-sense preventive measures include:

  • Transplanting sturdy plantlets grown on in pots, and not young vulnerable seedlings.
  • Rake over the soil and remove fallen leaves in winter so birds can eat slugs eggs.
  • Go out with a torch on mild, damp evenings and pick them off your crops.

Physical barriers

Mint acts as a deterrent in mulch

COPPER: Slugs and snails get a static electric shock when they cross copper tape – make sure it is the widest you can buy. Effective, but expensive. Stand containers on matting impregnated with copper salts or use bands like STV’s.

SHOP-BOUGHT REPELLENTS/MINERALS: Moisture-absorbent minerals/gel repellents can be placed around plants to create slug barriers (e.g. Westland Earth Matters Slug Blocker Granules, Growing Success Slug Stop and Vitax Slug Gone). Gel repellents (e.g. Westland Earth Matters Slug Blocker Gel, Doff Slug Defence Gel).

SANDPAPER: Make collars around plants – cut circles with a central hole from sandpaper. Cut a slit to the middle and pop it around the stem, laying the disc on the ground.

MINT/SAGE: Putting either or both of these herbs in your mulch acts as a repellent.

ROOIBOS/RED BUSH TEA: Used tea leaves deter gastropods and fertilize plants.

SHARP BARRIERS: Crushed eggshells, cinders, bark chippings, hair, pine needles, sharp sand, steel wool.

DESICCANTS: Ash (not from household waste, only wood fires), sawdust (cedar and oak), cornmeal, raw oats, bran.

DIATOMACEOUS EARTH: A fine powder of crushed fossilised sea algae. The sharp edges are like tiny razor blades to a slug but it has a similar effect on many small insects.

VASELINE/WD40: Smear/spray a 5cm band around the rim of pots.

Copper band review

Copper band
Himalayan lily protected by copper band

The STV Defenders’ Slug & Snail Bands went well on two of my most prized plants – the giant Himalayan lily (Cardiocrinum giganteum), and Hosta Empress Wu.

The extendable copper band, which lengthens to 55cm, generates a small repellent charge when a slug or snail attempts to cross it.

Reusable, the copper band is more versatile than sticky copper tape because it can be freestanding – that’s a bonus if you have a gravel garden like mine.

Multiple bands can be linked together, RRP £4.99 each. If you think that’s expensive, bear in mind these plants cost £12 and £10 respectively – better to protect your investments and enjoy such special plants?

Spray gastropods away

When in doubt, use garlic

GARLIC SPRAY: Crush two large garlic bulbs in a plastic bag with a rolling pin. Add crushed garlic to one litre of boiling water, simmer for 2-3 minutes. Once cool, strain the liquid through an old jelly bag/stockings into jars.

This liquid is concentrated – use two tablespoons in a 10-litre watering can and with a fine spray rose, water the leaves of your plants out of direct sun. Use every 14 days.

VINEGAR: Mix equal parts vinegar and water and spray it on snails/slugs.

AMMONIA: Use one part ammonia to four parts water in a spray bottle.

SALT: An old trick is to sprinkle it on slugs – keep salt away from plants.

Set liquid traps

beer table Hoegaarden
Seems like a waste of good beer…

BEER/YEAST & HONEY/GRAPE JUICE: Put out a large yoghurt pot half full of stale beer, boiled yeast, and honey, or old grape juice. Sink it into the ground so the lip of the pot is at ground level. Slugs and snails will fall into the mixture and drown. Check daily, empty and refill every couple of days.

PEELINGS: Place upturned half orange, grapefruit or melon skins, or inverted cabbage leaves near vulnerable plants. Check daily.

MILK: A beer trap alternative, but keep it covered if you have hedgehogs in your garden.

DRY DOG/CAT FOOD: Cut notches in a tin foil pie plate and put dry cat or dog food in the soil. Cover with the plate upside down lightly weighed down.

Sheep’s wool pellets

vitax-Slug-goneVitax’s Slug Gone are organic pellets made of sheep’s wool, which I’ve found useful, as long as you lay them thickly enough.

Put a layer around the plant and water – the pellets ‘self-felt’ and the fibres are an irritant to the pests, also absorbing moisture.

Biological controls

NEMATODES: Nemaslug is available in the form of a microscopic nematode or eelworm that is watered into the soil.

The nematodes (Phasmarhabditis hermaphrodita) enter slugs’ bodies and infect them with bacteria that cause a fatal disease.

Moist, warm soil (temperatures of 5-20ºC) is required, so it’s most effective during spring to early autumn.

Best results are achieved by applying in the evening; control may be less successful in heavy soils. It is unlikely to control snails, as they spend their time at or above soil level.

PREDATORS: Encourage thrushes, hedgehogs, ground beetles, toads, shrews and slow worms. Domestic chickens or ducks will also eat gastropods.

Resistant plants

Herbaceous perennials and annuals with some slug and snail resistance:

  • Acanthus mollis (bear’s breeches)
  • Achillea filipendulina
  • Agapanthus
  • Alchemilla mollis (lady’s mantle)
  • Japanese anemones
  • Antirrhinum (snapdragon)
  • Aquilegia
  • Armeria
  • Aster amellus, A.× frikartii, A. novae-angliae (Michaelmas daisies)
  • Astilbe
  • Astrantia
  • Bergenia (elephant’s ears)
  • Centaurea
  • Cynara cardunculus (globe artichoke)
  • Lamprocapnos spectabilis (bleeding heart)
  • Digitalis (foxglove)
  • Eryngium
  • Euphorbia
  • Foeniculum vulgare (fennel)
  • Fuchsia
  • Gaillardia
  • Geranium
  • Geum chiloense
  • Hemerocallis (day lilies)
  • Papaver nudicaule (Iceland poppy)
  • Pelargonium
  • Phlox
  • Potentilla
  • Pulmonaria (lungwort)
  • Rudbeckia
  • Scabiosa (scabious)
  • Sedum spectabile (ice plant)
  • Sempervivum (houseleeks)
  • Stachys
  • Tropaeolum (nasturtium)
  • Verbascum (mullein)