Slugs & snails live in damp, shady places among plants, plant debris and humus; crawling into crevices or beneath stones, pots, plastic etc... during the cold winter (soil temperature below about 5ºC & air below about 1ºC), dry summer (soil moisture below 26%) or sunny daytime. Only snails hibernate, sealing themselves within their shells. Slugs are more cold hardy & remain active in all but freezing weather. But severe weather will dramatically reduce their number as will a long hot spell, as they lose moisture rapidly. Marking snails reveals that they have pronounced homing behaviour, coming back to the same spot for shelter, clustering with other snails. They may feed several yards away. Food is located by smell. When damage becomes noticeable numbers are 50/60 per square meter and can increase to 100/200 during warm damp conditions.
To reduce slugs and snails by environmental means:
- Tidy the garden - reduce shelter & weeds. Avoid leaving pots, trays, plastic etc in cool damp parts of the garden. Though this may increase damage to adjacent crops which now attract full attention.
- Do not have hedges or grass borders next to susceptible plants.
- Digging /ploughing/rotivating before a frost.
- Digging /ploughing/rotivating in warm humid weather when slugs are active & near the surface exposing eggs / adults to predators.
- Where the problem is severe, digging can be followed by an evening application of aluminium sulphate, while slugs are active.
- Bare soil & frequent hoeing / rotivating exposes eggs & adults to predators & dehydration in dry weather. Eggs are laid shallow in the soil, about 30 / 200 together. They are white or transparent & 2 / 3 mm in diameter.Big changes in soil temperature & humidity (75% prefered) are fatal to the eggs. In drier weather they are laid deeper in the soil. Most eggs are laid May & September - hatching in 1 to 3 weeks.
- Finely worked soil leaves no clods or ground cracks for hiding.
- Draining wet & sour land.
- Liming sour & acid soil significantly reduces the population. Do not overlime as this may encourage snails.
- Improve soil structure with added well rotted compost, well worked in.
- An informal mixture of plants reduces damage - or companion planting or growing amongst wildflowers. Wildflowers can be allowed to self seed in the autumn (fall) - thinned & spaces cut for tender plants in spring.
- Lift crops promptly, especially potatoes.
- Carefully inspect newly bought in plants.
- Regulary inspect the underside of benches, pots, trays, water-hoses etc...
- Mow grass at night to kill slugs on the move!
- Absence of slugs & snails may indicate high levels of pollution!
Deep mulch beds or bare hoed beds?
Well rotted organic materials are less attractive to slugs than fresh materials & so are preferable for mulching. Mulches attract slugs with food and shelter. They also shelter many slug predators. Bare hoed beds make their lives hazardous. However it is easier in deep mulched beds to provide optimum growing conditions for most plants & grow them "hard". Barriers are easier to use on bare beds, but not impossible on deep mulch beds. All other methods work with either, though handpicking is quicker on bare beds; & natural predation is easier to encourage in deep mulch beds.
To overcome the disadvantage of mulches, plants need to be well grown, and perhaps planted out later, when larger and "hard". The requirements of particular plants should be studied & observed, & advice listened to.
Slugs & snails are attracted to eat tender young "soft" growth. They are far less interested in "hard" grown plants, produced by:
- An open sunny site.
- Optimum time of sowing / planting for the variety or species - when the soil is warm enough.
- Reduce the use of cloches.
- Optimum fertility / fertilizers. Not too much or too little feed.
- Use slow release fertilizers.
- Optimum water. Not too much or too little.
- Transplanted plants should be very thoroughly hardened off.
- Correct acidity / alkalinity.
- Good crop rotation, organic addition, etc.
- Do not grow susceptible plants or varieties. eg.: beans, peas, sweet-corn, squashes, marrow, carrots, celery, lettuce, brassica seedlings, strawberries, french marigold, pansies, primulas, nemesia, salvias, hostas, lilies, tulips, potatoes: "Redskin", "Maris Piper", "Cara" etc...
When sowing seeds or planting
- Cover dry soil beforehand if necessary, to keep it dry.
- Sow seeds in dry ground, only water bottom of drill before covering seed.
- When planting, only water near plant roots.
- Cover with cloche only if you intend to leave it on for a long time
- Toilet roll cylinders for bean transplants - planted with cardboard 2.5cm to 5cm above the ground as barrier & sacrificial slug food.
Grow vunerable crops over winter when slugs are least active:
- Spring cabbage
- Broad / Field beans
- Garlic, shallots, overwintered onion sets, welsh onions
- Parsnips sown early
If you have any comments, suggestions or tips please email Matthew email@example.com