Rough Scratchy Slug Barriers
It’s a mistaken belief that a slug will refuse to travel over sharp or abrasive surfaces. The fact is, a slug’s slime can allow it to glide unharmed across the edge of a razor blade!
So these rough barrier methods are far from foolproof and should been seen more for their ‘nuisance’ value. That said, many of them do offer a level of much needed protection for your plants, especially at that all important spring growing season when tender young seedlings are at their tastiest.
Ouch, ooh, ah, ooch, eek!
It’s a bit like hobbling barefoot over a stony beach – doable but unpleasant – and the slug would prefer not to do it. Traversing these rough surfaces requires the production of excessive amounts of mucus, or slime, to protect the slug’s soft underside. This depletes it’s valuable water reserves, potentially risking dehydration and death.
Slugs are more mobile in wet weather because their slime is hygroscopic; it draws in moisture. Slime becomes far more effective in wet conditions, and doesn’t deplete the slug of its resources nearly as much. That’s when you see them negotiating these more perilous terrains with such apparent ease.
Incidentally, it’s this hygroscopic property that makes slug slime so hard to wash off your hands. Adding water just makes it more slimy!
The best way to remove slug slime is to rub your hands together; it soon turns into little balls that can be discarded. You could also try white vinegar.
Slug barrier ideas
Here are some ideas you can use to create uncomfortable types of slug barrier. Most require reapplication of the protective material because it’s easily dispersed by wind or rain.
An old favourite is a circle of crushed eggshells, and these work well around single plants. It takes an awful lot of eggshells though, and the layer does need replenishing, so it’s a good idea to start saving them well before you need to use them.
As an added bonus, the calcium released from decaying eggshells helps ‘sweeten’ the soil.
A protective barrier can be made using finely crushed nut shells. Hard shells like walnuts work best. Start saving them at Christmas time and you’ll have enough by spring.
Ash and cinders
A barrier of ash and cinders helps keep slugs at bay. The cinders are rough to cross, and the powdery ash also acts as a desiccant.
Ash and cinders from a wood fire are preferable and can also add a little beneficial potash to the soil. Wood ash also helps ‘sweeten’ the soil, making it more alkaline which the slug hates. Avoid direct contact with plants because a concentration may be a little too caustic.
Coal ash should be used more sparingly because it also contains sulphur, making the soil more acidic, which the slug prefers.
Never put ash on the garden from a fire that’s burnt household rubbish or inorganic material. It could contain toxins.
Create a sawdust barrier around vulnerable plants. If possible, use sawdust from hardwood because it’s sharper and more abrasive. Some people say cedar works best.
Sawdust also acts as a desiccant, drawing moisture from the slug, which it doesn’t like.
Cut your own ‘anti-slug’ rings from a sheet of sandpaper and slip them round the stems of tender young plants. Or what about trying a sandpaper mat to stand a pot on?
Grit and gravel
Place grit around vulnerable plants. The sharp edges of finely crushed ‘horticultural grit’ work best. Don’t bother with coarser gravel because slugs don’t mind crawling over that.
A circle of sharp sand around tender plants can act as a slug deterrent. Another beneficial side effect is that it improves the drainage of heavy clay soils.
Don’t use builder’s sand or play sand; it’s far too soft.
Always use ‘washed’ sand, grit and gravel from a garden supplier when applying it to your soil, otherwise it could contain sea-salt. If in doubt, wash it yourself to be sure.
Hair probably doesn’t seem very rough or scratchy, but the cut ends are surprisingly uncomfortable to the soft underside of a slug. Have you ever noticed how irritating those little pieces of cut hair that slip down the back of your collar after a visit to the barbers can be...
Hair also sticks to the slug’s slimy body, entangling it and making it difficult to move about.
As a bonus, hair releases a small amount of beneficial nitrogen into the soil as it decomposes, so hair does have quite a lot going for it. The only real downside is that it’s not very practical in windy weather!
Diatomaceous earth has many uses, one of which is as a slug deterrent. A barrier of these minute razor-sharp particles is extremely uncomfortable for a slug to cross, cutting through it’s defensive slime and causing it to dehydrate and die.
Unfortunately, diatomaceous earth is a double-edged sword. Although it’s perfectly harmless to plants, animals and humans, it can be hazardous to other small insects, some of which are the gardener’s friends. So it’s best to use it sparingly and selectively.
The fine powder can be irritating if inhaled, so it’s recommended to use a mask when using diatomaceous earth.
Try standing your pots and containers on a mat of steel wool. Slugs don’t like crawling over it.
A mulch of pine needles can form a natural and effective prickly barrier, keeping slugs away from your plants.
Use a coarse mulch of something like cedar or oak bark chippings. Try to limit the use of organic mulches until plants are more slug hardy because the damp decomposing matter actually attracts slugs with food and shelter.
A carpet of thorny prunings can help keep slugs away from your plants. It makes a good cat deterrent too. But be aware that when dry and dead, these can become very brittle and break into small pieces. It’s very easy to get a nasty thorn in the finger while tidying the garden... Ouch!
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British gardeners use over 400 billion slug pellets every year