The sight of verdant young shoots pushing through warming spring soil lifts the heart of every gardener. After weeks of anticipation the garden is finally moving. We rush to the greenhouse and start frantically sowing, gleefully admiring trays brimming with new seedlings. Hoes and rakes are joyfully unleashed from dark sheds, the soil is tilled, seeds are scattered. At the end of the day, as sunlight rakes across our tired but satisfied brows, visions of perfect lettuces, juicy peas and drifts of flowering annuals dance before our eyes. Spring – the season of optimism!
But behind that optimism is a hidden anxiety. There is something nasty lurking under the leaf litter at the back of your mind. And suddenly, in one damp night, swathes of innocent baby seedlings are ruthlessly massacred, eager buds nipped off in their prime, precious young shoots ripped to shreds. Yes! Those monstrous molluscs have returned: Slugs and snails.
Spring into action against slugs and snails
As temperatures rise, slugs and snails emerge from hibernation where the ability to super-cool their bodies has protected them from freezing. Meanwhile, generations of eggs laid in the autumn are busy hatching throughout April and May. All of these animals emerge with raging appetites and, as the spring garden serves up a banquet of soft and succulent food, who can blame them for gorging at the feast?
From 1 April 2022 it is now illegal to sell and use metaldehyde slug pellets. So, whether you like it or not, this particular weapon can no longer be part of your armoury against the gardener’s number one enemy. British gardeners have been using some 650 billion slug pellets per year – and there is no doubt about it – they worked. Sadly, they worked rather too well. Only a small amount of metaldehyde is needed to poison or kill non-target animals and as the pellets included a bait, every animal which occupies your garden – birds, frogs, toads, newts, hedgehogs, slow worms, mice, even your pets – was at risk.
The good news is that there are many alternative and safe slug and snail deterrents. But which actually work? Being prepared in advance of the enemy is crucial – so let’s examine the options both silly and sensible – and whilst we’re at it, take a closer look at these much-maligned molluscs, delving into dark, damp corners to uncover some of their slimy secrets.
Hand to hand combat
Post-war gardeners were made of stern stuff. My mum would pluck a slug from the ground, confront it eyeball to eyestalk and then abruptly slice it in two with her secateurs. I don’t count myself as a squeamish gardener, but this is a bit too much for my stomach. Neither am I that fond of her other strategy: the nightly ritual of slug-stalking with a salt cellar which the following morning would leave hazardous pools of slug-gloop along the path awaiting my young unshod feet.
I am however partial to the satisfying scrunch of crushing snails beneath my boot. But I confess to being a cowardly killer, as I prefer not to look too closely at my victims as they flinch under my boot. As well as their eyes, snails have light sensing cells dispersed all over their outer skin which enables them to quickly react to the hovering shadow of a murderous hand or boot. Other suggested molluscan murder methods include collecting them all in a bucket. Exactly what you do with your bucket of slugs and snails afterwards I do not know or care to contemplate.
Are these methods effective? Well, they certainly satisfy the gardener’s thirst for revenge. But do they make any significant dent in the population of molluscs which are busy consuming your garden? The problem is, although you may not find these molluscs attractive, they find each other positively irresistible. Both slugs and snails are hermaphrodite, which is a distinct advantage for such slow animals that might otherwise have difficulty bumping into the ‘right’ partner; and both enjoy very elaborate courtship rituals which can go on for hours. In fact, gastropods have voracious appetites for love as well as food and can boast of very adventurous sex lives, so adventurous that the next time I look a snail in the eye both of us might blush. All this romance means that the average garden has 20,000 slugs and lay as many as 200 eggs per cubic metre. So I’m afraid you may have won the battle, but the slugs have definitely won the war.
Create a slug zone
One suggestion I have come across on the internet is to ‘deliberately attract slugs’ to an area of your garden away from your target plants and then to go out and collect them at night. Gardeners World suggests “using something they’re attracted to – old veg leaves, dried cat food, bread rolls, oats or bran”. To me, this sounds like a very good way of attracting rats as well as molluscs and given that rats have a considerable speed advantage, I suspect that both slugs, snails and the gardener are likely to end up disappointed by the results.
It also raises the same tricky problem encountered above – what do you do with your bucketful of slugs and snails? One traditional solution has been to lob them over the neighbour’s fence. If you are having a boundary dispute with your neighbour this will probably give considerable satisfaction, until that is, those cunning slugs and snails find their way home. Unfortunately, scientists have discovered that snails are equipped with a homing instinct. This means they need to be hurled at least 20 metres away to ensure they won’t find their way back – a feat which would require the arms of an Olympic shot putter.
I’m left with a sinking feeling that this project is doomed to backfire – the neighbour is enjoying a garden freed of slugs, snails and rats whilst I’m saddled with a bucketful of slimy slugs and snails and a cold walk in the night to dispose of them.
Eggshells, sawdust, coffee grounds, wood ash, human hair, grit, etcetera, etcetera
Sorry, but all of these methods are perfectly useless. This is because slugs and snails are equipped with a super power: slime! Acting as both an adhesive and a lubricant, this slime has miraculous elastic properties and the ability to change its consistency when pressure is applied. Get slug slime on your skin and you will find it a devil to wash off due to its supreme stickiness and impressive ability to hold water. Scientists have even taken inspiration from slug slime to develop medical glues which will bond wet tissues and stem bleeding. Even hedgehogs find slug slime troublesome to deal with. This video by Julia from The Hedgehog Diaries shows a hedgehog de-sliming its slug meal by rolling it on the ground!
Dr Hodgson of Exeter University has discovered that snails use up to 30 percent of their energy in slime production and reports that ‘snails move in convoys, piggy-backing on the slime of other snails to conserve energy’. Slime not only assists movement but is also designed to prevent injury when molluscs move over rough surfaces. Their sublime slime means that slugs and snails can happily glide across razor blades and they will be laughing off your puny human efforts to deter them with mere eggshells.
Put aside your eggshells and coffee grounds and try wool pellets instead. If you find wool jumpers itchy, then so do slugs! Wool fibres are highly hygroscopic, meaning they absorb moisture. This, plus natural sands and grits in the wool and salts from sweaty sheep, sucks up slime and causes irritation to the slugs so they crawl off in search of easier food.
After placing them around the base of the plant the pellets are thoroughly watered. This causes them swell and bind together forming a dense matt which isn’t disturbed by wind or rain. Although wool pellets are quite pricey the mat will last for up to 12 months and has the bonus of acting as a mulch which will supress weeds and retain moisture, breaking down naturally in the soil to slowly release nutrients.
I planted out a lot of sunflower seedlings last year and tired of watching each one being felled by marauding molluscs I tried wool pellets. I’m pleased to report that they were a resounding success. They need to be piled up in a wide, thick barrier ( at least 4inches (10cm) wide and a few inches deep) so are good for protecting individual specimens such as hostas, delphiniums, sweet peas and lupins but not so useful for long rows of seedlings.
Grazers offer a range of organic pest-deterrents in a liquid form which are based on calcium, with different formulations tailored to different pests. I’ve certainly had success using Grazers to deter rabbits and pigeons, so their slug and snail formula looks a promising bet. What I have found is that for Grazers to be successful you need to apply it thoroughly and repeat spray at intervals. How often you need to re-apply will largely depend on rainfall, time of year and growth rates so it varies from several days to a few weeks. Fast growing young plants with soft tissues which are subject to heavy spring rains will need more frequent applications. If you are only treating one or two plants then a handheld sprayer is fine but keen gardeners would be well to invest in a pressure sprayer for this task. This allows you to make up a tank of mix and then grab it and speedily spray your vulnerable plants whenever required.
The calcium contained in Grazers is absorbed through plant leaves and stems into plant cells. It doesn’t kill slugs and snails but makes plant tissues distasteful so they will seek other food sources. It takes a little while for the calcium to be absorbed and moved through the plant, so if you are transplanting vulnerable young plants from the greenhouse to their outdoor positions, it’s a good idea to treat them with Grazers for a few days prior to doing so. Price wise, Grazers is a relatively economic option, but it obviously requires more labour than putting down wool pellets. However, it’s better suited to large areas of crops or ornamentals.
Gastropod grazing habits
Not for nothing are slugs and snails known as ‘gastropods’ – literally an ‘eating foot’. These animals have evolved into highly efficient munching machines and they are not easily put off their meals. Grazers is the only commercial product which makes plant tissues distasteful to them. Both slugs and snails are equipped with a ribbon-like tongue called a radula which is covered in thousands of tiny teeth, neatly arranged in rows. In fact, the garden snail has about 14,000 teeth! By grinding the radula against its horny jaw, the slug or snail rasps at its food. This causes the ragged abrasion of plant surfaces which is characteristic of slug and snail damage. It also enables them to grind their way through tougher foods like your potato tubers. They may lose a few teeth in the process, but new ones quickly regrow in their place. Once past the mouth food enters a holding bay or ‘crop’ so slugs and snails can happily ‘eat on the run’, bolting down your entire tray of seedlings, rapidly followed by seconds and pudding before retreating beneath the tray to digest dinner at leisure, in the dark and hidden from predators.
Organic-approved slug pellets
What’s in organic slug pellets and how do they work?
Numerous brands of organic-approved slug pellets are available including:
All of these products are based on ferric (iron) phosphate which is bound to a cereal-flour based bait. Iron phosphate affects the metabolism of calcium in the gut of slugs and snails causing them to stop feeding and die within three to six days. Any uneaten pellets will slowly break down releasing phosphate and iron which will be taken up by plants as nutrients.
Effect on earthworms
These pellets are harmless to mammals but there is one downside – they can be harmful to earthworms. Alongside ferric phosphate, the pellets contain chelating agents and are consumed by earthworms which causes them to feed less, lose weight and die. The power of humble earthworms in maintaining a healthy soil ecosystem is not something to be casually dismissed, so it is essential that gardeners use these pellets responsibly.
I wince when I see people pour gluts of pellets all over the place as this really isn’t necessary – the pellets are baited and so will attract slugs and snails to them. These molluscs are equipped with incredibly sensitive taste and smell organs in their lips and tentacles which can detect minute chemical traces in their environment. Slugs and snails find potential mates by sniffing out and following mucus trails and will back track along their own scented trails to find their way home. So, if you are going to use organic slug pellets, do so sparingly, just using 4 or 5 in an area the size of an A4 piece of paper.
Nematodes: The slug’s nemesis
What are nematodes and how do they work?
Professional gardeners have been using living organisms to control pests, known as ‘biological control’, for many years. They are now readily available to amateur gardeners, and if you haven’t tried them yet then you are definitely missing a trick! Nematodes are microscopic worms which are naturally present in the soil and act as parasites on other living organisms. The great thing about them is that they are host-specific and so non-target species are left unharmed.
There are nematodes for a whole range of pests and they all have distinctly unpronounceable and forgettable names. Phasmarhabditis hermaphrodita is the one for slugs, conveniently sold under the moniker ‘Nemaslug’. These tiny worms with a big name are certainly the slugs nemesis. They enter the slugs body through its breathing pore, multiplying rapidly and causing them to develop a swollen mantle. The sick slug immediately goes off its food and often remains underground. So, although it takes between 7 to 21 days for it to keel over and die, damage to your precious plants is immediately reduced. Once the slug dies the nematodes tuck in and feed off its remains. They go on to produce another generation of hungry slug-killers which travel through the soil to hunt down new slug hosts.
Application and timing
Nemaslug is effective but it must be applied correctly and timing is crucial. The sachet containing the nematodes is mixed into water and applied onto the soil using a watering can or garden hose applicator. The soil temperature needs to be consistently above 5°C but you also want to apply it as early as possible in the spring to catch the first generation of young slugs before they turn into larger adults which are more resistant to infection. One application provides up to 6 weeks of control so, several applications are needed during the growing season. As Nemaslug is a live product with a shelf life, (it has to be stored in a refrigerator on receipt), the packet includes a small calendar to record applications and remind you when to order your next batch.
Good against slugs but not snails
Nemaslug is effective on all pest slug species and grey field slugs are especially susceptible which is good news as they are the most damaging of all garden slugs. However, if snails are your biggest enemy then Nemaslug won’t be much use. Although nematodes can kill snails, they tend to evade infection due to their largely surface-dwelling nature.
Being ugly, slimy and homeless, slugs have few fans, and seem to come in for the most blame. Meanwhile the snail, with its ingenious and pretty armour, its shy ‘peak a boo’ behaviour and the fact that the shell provides a convenient and dry hand hold for curious humans, has a slighter cuter reputation. However, of the 30 plus species of slugs in Britain, only 4 are really garden pests feeding off living plant material, the remainder prefer munching on dead organic matter. If you have a limey soil, point the finger of blame at snails instead. They prefer calcareous soils which provide the necessary calcium to build their shells.
Not so effective on heavy soils
Nemaslug is more effective in freely draining soils than heavy clays, as these allow nematodes to easily move about and find their hosts.
Harmless to earthworms
Nemaslug has the advantage over organic pellets in that it continues to work well in wet weather and numerous experiments have demonstrated that it is completely harmless to earthworms along with insects and other organisms.
Beer traps are a well-known traditional slug and snail deterrent but they are a method which I definitely can’t advocate. Slugs and snails can sniff out fermenting beer from long distances and will be attracted to your boozy garden often without actually drowning in the beer, so you are likely to end up with a bigger population of molluscs than you started with. Meanwhile, a host of other beneficial insects will also be attracted to your traps and meet a sticky end. Personally I think it’s a waste of beer. Let’s move on!
Slug and snail collars
Slugs and snails aren’t equipped with much in the way of brains, instead they have ‘ganglia’ – basically bundles of nerve cells – which may explain why they have a hard time negotiating these plastic collars. When they reach the overhanging lip these simple-minded molluscs get confused by this apparent ‘dead end street’ and fail to find their way to your tasty plants. There are undoubtedly some molluscs out there with a better sense of direction, so it isn’t a 100% fool proof solution, but it avoids this use of any chemicals and requires minimal effort. Although I think their appearance is unsuited to the ornamental garden, this is a cheap and easy way to protect your soft stemmed vegetable crops.
Slug and snail control: A military strategy
Use a combination of methods
In the war against slugs and snails it pays to have a co-ordinated strategy, employing all of your cultural, chemical and physical strategies to defeat these resilient garden adversaries. Don’t rely on just one of the methods above, which all have their advantages and disadvantages, but use them in tandem. Use an early application of nematodes to protect vulnerable root crops, such as potatoes, across a wide area of ground. Apply Grazers to leafy veg such as brassicas. Meanwhile, protect your ornamentals with Ferric phosphate and wool pellets.
Grow your seedlings on
Grow seedlings on until they have reached a reasonable size and their stem and leaf tissues have toughened up a bit before planting them out. Greenhouses can quickly get too hot in spring sunshine even when the ambient temperature is cold. Seedlings raised in excessively warm conditions grow very soft and leggy – perfect food for slugs and snails. Ventilate your greenhouse as much as possible to keep temperatures at a reasonable level and harden off seedlings in a slug-protected area (see below) before they go outside.
Concentrate your efforts
Pay especial attention to your nursery areas where seedlings and young plants are placed and concentrate your efforts on these zones, using Ferric phosphate pellets sparingly to protect them. Reduce any hiding places in these areas by keeping them tidy and removing debris and leaves. Pay attention to crop margins which are adjacent to nearby cover such as hedges or long grass.
Check your seed trays
Slugs and snails love to hide beneath seed trays and pots so check underneath them everyday.
Don’t use high nitrogen fertilisers too much
Slugs and snails will go for soft juicy growth which is exactly what high nitrogen fertilisers promote. Aim instead for slow, steady growth. Where necessary use organic slow-release fertilisers or specialised feeds such as Chempak Low Nitrogen (good for firming up vegetables and vulnerable plants such as lupins and delphiniums), or Chempak High Potash (to encourage flowering rather than leaf and stem growth).
Water in the morning
This will enable the ground and foliage to dry out before foraging molluscs come out at night.
Be vigilant during wet weather
After every bout of rain check and renew your slug and snail defences where necessary.
All of the animals listed below eat slugs and snails, so it makes sense to recruit them as your allies. Our wildlife gardening guides provide plenty of tips for encouraging them into your garden.
- ground beetles
Avoid the plants most vulnerable to slugs and snails
If slug and snail warfare isn’t your thing, then don’t bother with the plants listed below :
- Soloman’s Seal
- Sweet peas
Slugs and snails are here to stay!
There is no way of completely eradicating slugs and snails and if we could, our gardens would be in a terrible mess. Slugs and snails are primary consumers, munching through organic matter, fungi and algae and making it available to smaller organisms. Without them, we would literally be surrounded by rubbish. Think of them as one of nature’s dustmen, indiscriminate but efficient. They also form an important part of the garden eco-system, providing food for all sorts of animals. Concentrate your efforts on young seedlings and the most vulnerable plants, and accept that slugs and snails will always love your garden as much as you do!
Published at Thu, 07 Apr 2022 07:34:48 -0400