Why the RHS thinks we should make friends with slugs

They can act as “nature’s clean-up crew”: here’s how to distinguish between helpful and hateful slugs

Gardeners are very in tune with the natural world. They notice the changing climate and they’ve realised that there are fewer birds, bees and butterflies. And it’s not their imagination: in October 2021 the Natural History Museum, in collaboration with the RSPB, declared that the UK has an average of only 53 per cent of its biodiversity left.  
Gardeners do their best to redress the balance, by making wildflower meadows, feeding their birds, and installing hedgehog homes, bird boxes and bee hotels with the aim of helping wildlife. And yet, many gardeners still feel compelled to use slug bait, in order to protect their vulnerable petunias and hostas. The word “organic” emblazoned across these so-called green products gives the impression that they’re eco-friendly, but their use interrupts the natural balance and disrupts the complex food webs found within every garden, however small. 
It’s why the Royal Horticultural Society (RHS) has joined forces with the Wildlife Trusts to encourage people to “make friends with a mollusc”, rather than killing what it calls “nature’s clean-up crew”, pointing out that slugs and snails consume dead plants and animals, and provide a food source for animals and birds. “By learning to appreciate and coexist with these creatures,” says the RHS, “gardeners can adopt a more environmentally friendly approach to gardening.” 
Slug bait is indiscriminate in the way it works, killing most slug species. It also gets into water courses, which is why blue metaldehyde pellets were banned here in 2022. According to the Environment Agency (EA), between 2009 and 2011 concentrations of metaldehyde used by farmers were found in 81 of 647 (that’s one in eight) reservoirs, rivers and groundwater in England and Wales from which drinking water was sourced.
In 2013, Natural England and the EA revealed that homes in Essex and Suffolk, drawing supplies from the River Stour, had to drink tap water containing 100 times the recommended level.
Following the metaldehyde ban, gardeners have turned to various types of slug pellet, including iron phosphate. However, these products still eradicate most species of slug and some of those creatures could have been very useful to you: They are detritus eaters, and might have cleared up rotting plant material and fungi.
Such decaying materials are targeted by slugs because they contain more protein than fresh plant material. Slugs also fertilise the soil, so they don’t necessarily deserve a slimy death at your hands.
But even if you hate slugs, using bait may not be the most effective way of keeping them under control – in fact, it may deter ground beetles, which, along with their larvae, are the best predators of slugs the gardener has. Other creatures consume slugs too, and they include hedgehogs, who turn to them when their preferred diet of beetles, caterpillars and earthworms has dwindled.
Frogs also take lots of slugs in late spring, to restore themselves after a hectic breeding season. Blackbirds are very adept at tackling slimy smaller slugs by dragging them across the lawn. Female birds seek out empty snail shells and eat them, to boost their calcium before egg laying.
There are lots of strategies that help the gardener to tackle slugs, without resorting to slug bait. If you’ve grown bedding plants in your greenhouse, or bought them from a garden centre, always harden them off for a week to toughen up the foliage. The garden table works well for me.
If you lose your petunias year after year, go for slug-proof pelargoniums and plectranthus instead. After all, our planet’s more important than your petunias. Avoid using nitrogen-rich plant food because the lush, rapid growth it promotes is a gourmet meal for gastropods. Use a potash-rich tomato food instead as it toughens up the foliage. 
Try to avoid containers with a lip because the area underneath is a perfect refuge for snails and slugs. Hostas, the Holy Grail of the snail, definitely need straight-sided pots. If you’ve got hostas in the ground, hoe around them to disturb any eggs or slugs in the soil.
Raking through the soil also helps and your resident robin will be extremely grateful to you. Avoid seed trays with large indentations in the base, because slugs find a refuge under your seedlings. Go for flat-bottomed trays instead. 
Frisk your garden in winter because a container can attract a cluster of hibernating garden snails. You may want to destroy the snails you find, although it’s worth remembering that the large brown snails are the preferred food of the song thrush.
Thrushes will take smaller snails with thicker shells, but only if they have to. These smaller snails, with banded cream shells, are useful detritus eaters so I always leave them to their own devices. Poke about in evergreen kniphofias, phormiums and colchicums (autumn crocus) too. Snails often hibernate there in winter. 
In spring, I change to hands-on tactics. I have scaffold planks between each of my 8ft x 4ft vegetable beds. These are lifted every few days and any slugs found are examined to see whether they are nice or nasty (see below).
My most vulnerable vegetable plants, principally my runner beans, are protected by two decoy plants, “Salad Bowl” lettuces and taller single-flowered African marigolds. Slugs prefer both of these to my beans. As dusk falls, I’m armed with a torch, gloves and a jam jar. I stargaze at the same time. That’s the time to go on a slug hunt. Also try to water in the mornings, so that the soil dries out before the slugs appear. 
If you have a real problem, there are plenty of garden plants that are shunned by slugs. They ignore anything silvery and aromatic, because the leaves have a pungent, oily coating which they dislike. Lavender, rosemary, achillea, salvias and nepeta are all safe from them.
Certain plants are full of toxic alkaloids and that includes members of the buttercup or ranunculaceae family. They do not touch hellebores, aquilegias, aconitum , Japanese anemones or clematis. They don’t munch through hardy geraniums, astrantias, euphorbias, peonies, penstemons, asters, foxgloves, heucheras, verbascums, veronicas or sedums. They’re all safe from attack. 
It’s a good idea to collect leaves from your garden once they fall, because you’ll often find newly hatched baby slugs attached to the undersides. I’m keen to protect my trilliums, which are slug prone, so my woodland garden is tidied up in autumn and the collected leaves are made into leaf mould. 
So, abandon the bait and leave your slugs for the hedgehogs, frogs, birds and beetles and all the other creatures. Let your song thrush get the benefit of your snails. Big-boot the baddies, but let the others be.
There are around 43 types of shell-less gastropods in the UK. Of these, 21 are found in gardens – and seven can be troublesome 
(Deroceras reticulatum)
This small, light-fawn slimy slug survives low temperatures and breeds throughout the year. It can scale your runner beans and it loves to hide in lettuces. The milky mucous puts most predators off, but not ground beetles.
(Arion hortensis group)
This group of smaller slugs have wrinkled backs with no prominent ridge. The body is dark and the underside is yellow to orange in colour. They have distinctive yellow-orange mucus and are only active once temperatures rise above 5C. 
(Tandonia budapestensis)
This brownish-grey slug penetrates your potatoes. It curls into a sickle shape above ground, but most of the time it’s underground. It has a ridge and a creamy line along its body. Lift your potatoes before October.
(Ambigolimax valentianus)
More of an emerging problem, but it’s already arrived in my garden. It is medium-sized with faint lines on the mantle, which extend along the body. Often found near greenhouses.
(Limax maximus)
A large, striking slug with a brown or grey body and brown or black spots or blotches. They eat other slugs, including the baddies, and will clear dead and rotting plants, as well as fungi. 
(Boettgerilla pallens)
This slender grey or brown worm-like slug eats carrion, earthworm excrement and decaying organic matter. It will burrow down to 2ft and can be found under logs and stones. It also consumes slug eggs.
(Limacus maculatus)
Not a known pest of live plants, but it will regularly eat mould and algae and is often found within compost heaps. Commonly creeps into the home in search of pet food. The creamy grey background has irregular green blotches. 
(Arion ater)
These large round backed slugs come in brown, black, grey, green, orange or red. There is no keel and the contracted body is bell-shaped and the mucus colourless. These large, detritus-eating slugs often appear on lawns after rain.
For further research download Identifying British Slugs by Brian Eversham of Bedfordshire, Cambridgeshire and Northamptonshire Wildlife Trusts (wildlifebcn.org)