Last updated March 2018
Slugs, and to a lesser extent snails, cause the most damage in our garden, so it’s fortunate for us that there are greengrocers, as we find it a losing battle trying to grow our own five-a-day.
The snails have diminished since magpies moved in, and we’ve seen magpies eating slugs too, but it’s going to take them and the thrushes a long time to get through the healthy population lurking under the leaves.
Unfortunately it’s not always the big ugly slugs that do the damage but quite small ones that live in the soil and emerge by the plant stem to attack it or the leaves, usually after dark. Spring and autumn are the worst times, when there’s high humidity or heavy rain, and of course these are the sowing and planting seasons. Then there are the snails, who have no fear of dry weather. So what to do, especially if you are into organic food and growing?
Try the following, and let us know what succeeded for you.
1. Cultivation to control/kill slugs/snails
2. Give the plants a chance
3. Slug/snail removal
4. Predators for biological control of slugs/snails
5. Slug/snail barriers
6. Grow slug-resistant plants
7. Grow sacrificial plants to divert slugs/snails
8. Slugicides/molluscicides – chemical slug/snail killers
9. Don’ts when controlling slugs/snails
Cultivation to control/kill slugs/snails
Keep the ground cultivated – cultivation in cold weather exposes slugs and eggs to freezing conditions. Also a fine seedbed means less clods of soil for slugs to hide in. It’s important too to choose your location – don’t sow crops close to hedges or shrubbery where slugs can easily migrate from.
Unfortunately mulches and organic matter provide lots of nooks and crannies for slugs to survive in, so make sure they are not too close to the stems and leaves of vulnerable plants.
Give the plants a chance
Grow plants on until their stems are a sturdy size before transplanting into the garden. Avoid bare-root transplanting as plants are vulnerable until their roots become established and the plant can start growing again. It’s better to plant out a large plug or a pot-sized rootball.
Slug and snail removal
Snails can be crushed if you’re not squeamish, and slugs picked up and dropped into a container of very hot water to kill them. Then dump the bodies for the birds to hoover up. Salty water is another option, but salt can damage plants and birds.
Some people cart away live slugs and snails to dump them a long way away (they will come back if you throw them over the fence!), which eventually reduces the numbers, but if the food is still there in your garden, the numbers are bound to build up again.
Whichever method you use, you have to be persistent, but take heart because it does work. To be more efficient, attract the slugs and snails to one place for collection. Slugs will stay out of the sun and hidden from predators, so some grapefruit skins (halves turned upside down), or large leaves such as cabbage or rhubarb, make good traps that you can clear daily. Another advantage of these types of cover is that snails are less likely to dig down into the soil’s surface out of sight, so they are easier to find and dispose of. Otherwise, you’ll be forced to go hunting at night, especially damp or rainy nights, to find them all.
You could also try drowning them in sunken pots, saucers, or specifically designed containers from Thompson and Morgan. Leave the rim of the trap about 1cm (half an inch) above soil to avoid trapping beneficial insects trundling by, and add bait to entice slugs into the liquid. Baits include beer, but if you object to giving them your drink in addition to your veg, you could use a yeasty mixture (Marmite or baker’s yeast) in water. Apparently dried cat food is also effective, but we haven’t tried that.
Predators for biological control of slugs/snails
Birds and hedgehogs will prey on slugs, so encourage them both. Cultivate the ground to attract birds to peck through the soil, where they will find these pests. Chickens and ducks are also great slug snafflers but caring for them might not be easy, depending on your garden and your situation. Nematodes (tiny parasitic worms), available from Harrod Horticultural, are very effective at killing slugs but need applying every six weeks, so you have to be organised. Although they might appear expensive, if you compare the cost with the loss of plants and the amount of slug pellets you would have used, you could be surprised.
Most (home-made or mass produced) are based on the theory of providing a dehydrating layer that dries up the slug’s slime or acts as an irritant to them so they avoid the area, or produce more slime and become dehydrated, which slows them down. Materials suggested include eggshells, grit, or vermiculite (but this blows away easily); there are also many specific barrier products. However, assuming the theory is correct (a big if), these layers won’t stop the pests popping up from underground.
Containers are easier to protect with Vaseline or WD40 or similar on the container’s sides to make a very slippery surface that slugs and snails cannot move across. Copper tape makes a more permanent barrier around the pot – it gives the slug a shock. Just ensure that overhanging vegetation doesn’t bridge the copper otherwise the creatures can bypass the deterrent. However, don’t expect it to always affect slugs that arrive from undergound.
Grow slug-resistant plants
Annoying advice, but there’s no point trying to grow a range of slug favourites in a slug-riddled garden – you’re just making life hard for yourself. This advice is also of little use to veggie growers either, but fruit bushes and trees can give you the satisfaction of food production without a war on slugs. Of course, then blackbirds and wasps become your obsession…. Actually there are some plants that are noted for their slug resistance, such as those with tough, hairy or scented leaves (including many herbs). Also certain varieties of vegetables are less attractive (meaning nibbled but not destroyed) such as particular slug-resistant potatoes. Also there is a new (for 2018) New Zealand spinach Tetragonia tetragonioides from Unwins that is worth a try as they claim it ‘shuns slugs’.
Encourage birds and toads in the garden by providing some water for them and some cover, but not too much cover for the slugs. Yep, contradictory advice. We find our pond more useful for drowning the slugs that we pick up than for its frogs, who don’t seem to snack on slugs enthusiastically enough.
Grow sacrificial plants to divert slugs/snails
Grow some plants that slugs and snails love above all others, so that they leave the rest of the plants for you. Try something with soft leaves such as a row of lettuce, or a hosta variety (but not one claimed to be slug resistant). We’ve read that lawn chamomile (dwarf Chamaemelum nobile ‘Treneague’) is extremely attractive to slugs, but haven’t grown this so can’t confirm. It is non-flowering so you cannot buy seeds, only plants.
Slugicides/Molluscicides – chemical slug/snail killers
Slug/snail deterrents and killers (therefore pesticides) available to gardeners in the UK (e.g. from Thompson and Morgan) usually contain either metaldehyde, iron (ferric) phosphate or aluminium sulphate. Most slug pellets don’t kill slugs directly but dehydrate them so they stop moving and then dessicate in the sun (but if there’s no sun, they recover and slime off to munch another day). Another point to remember is that slug pellets contain bait, so if you are over-generous with the stuff, you’ll attract even more to your plot.
Unfortunately, heavy rain dissolves the pellets and washes them into the soil where they are not effective, although there are some rain-fast types available. If using slug killers around edible crops, be sure to adhere to the instructions and only apply the recommended number of times.
If used at the correct level, there’s little evidence of harm to slug-eating creatures, but the problem is that dogs in particular can develop a taste for metaldehyde and go around the whole garden snuffling them all up, or worse still, get into the box or bag. Any quantity will kill or seriously harm a pet (or person!) so keep the bag or box safely locked away.
Metaldehyde is not acceptable for organic growers, and although iron phosphate is permitted by the EU, it is only reluctantly accepted by the Soil Association, with provisos. Aluminium sulphate kills on contact – it is not organic either but the RSPB considers it one of the less risky chemical killers. Iron (ferric) phosphate is probably the least problematic of the three. So-called ‘organic’ slug killers are available from Thompson & Morgan or Harrod Horticultural but check the ingredients are the ones you want before buying.
A relatively recent product, based on a trace element that repels slugs and snails, and is safe for all life, is Grazers’ G2 . We plan to give it a go.
Another concoction with good reviews, according to internet forum contributions, is garlic. Either garlic oil on the soil around plants, or garlic water (boil up some crushed cloves of garlic in water; strain the result; store as a concentrate; apply diluted mix to leaves freqently). Be careful to dilute out the concentrate to avoid damaging the leaves, and don’t apply in sunshine otherwise the leaves could be scorched. We’ll be trying this too.
…use old carpet or plastic sheeting as a weed suppressant because slugs hide underneath where predators can’t get at them, then venture out at night to eat your plants.
…water your plants in the evening, otherwise you’ll encourage slugs and snails. Water in the morning or during the day so excess on the leaves and soil can drain/evaporate away.