Fighting the slug and snail takeover

I don't know about your garden but the molluscs are taking over in mine. We had a wet winter in which it never really got properly cold and so hibernating slugs, snails and their eggs didn't get killed off in their usual numbers. Now after a reasonably fine spring, we had a warm wet start to the summer. Lots of lush green leafy growth means lots for slugs and snails to sink their teeth (oh, yes, teeth)  into. One single slug or snail can reduce a courgette or lettuce seedling to a bare stalk in one session: in addition to a rough tongue called a radula, they also have thousands of tiny denticles, or tooth-like protusions. 

I must have tried every single slug/snail barrier or killing method known to mankind over the years. The problem is that there is no one ideal solution for all situations. Not everyone likes the idea of killing the pests in large numbers. One of the easiest ways to get rid of slugs and snails is to scatter slug pellets around your precious plants, yet it's well-documented that slug pellets will harm other wildlife as well. I only use them when the slug numbers are overwhelming and only under netting or in the greenhouse to try to minimise the danger of anything else ingesting them. I wish I didn't use them at all and I dislike dealing with the messy slimy death the pellets cause.

You don't, however, have to kill your slugs and snails: there are various ways to deter them, whether through physical barriers, or what I think of as diversionary tactics. I've found that repelling them without killing them tends to work well in years when the slugs/snails are not around in huge numbers; in very sluggy years like this one, they will just slope off to eat something else. I don't, for example, usually bother with slug protection for my chilli plants: slugs and snails don't tend to find them very appetising. This year, I've lost several chilli seedlings to slugs and snails: there are so many more of the pests and if they can't get at the salad leaves, or the young courgettes, they'll chomp down on whatever they do find. It's tempting just to pick them up and throw them over the fence, but both slugs and snails apparently have a homing instinct and they will just come back, even if somewhat slowly.

Caught in the act: young courgette and squash seedlings are a
favourite target, also salad leaves, brassicas, and my wasabi plants,
which I have to keep almost hermetically sealed away from
both slugs and snails.

One of the most attractive options (to me anyway) is to biologically control them with nematodes: near-microscopic organisms which live in the soil, and will eat into slugs and kill it. The nematodes do not interact like this with anything else, so are harmless to other wildlife, and the slugs are eliminated (good), yet the killing happens remotely and invisibly to me (even better). But even this is no cure-all: it's expensive, it needs to be done every six weeks or so throughout summer, and is really only effective against slugs, because the nematodes work in the soil, and snails tend to live above ground. 

The best solution of all, if available to you, is to create a slug/snail-hostile environment as naturally as possible. A pond with frogs, a resident hedgehog family and a population of thrushes and other slug-eating birds will help to keep numbers to a minimum. And one thing I've learned recently is that I shouldn't really be aiming to eliminate the molluscs altogether: only some of the 30 different slug species that live in the UK eat your tender vegetables, they and the rest will also feed copiously on decaying vegetable matter and so are an important part of your overall garden ecosystem.

In a dry spell, the slugs and snails seem to disappear. But if you overturn
pots, peel back black plastic or look underneath decaying wood, the
chances are you'll find them hiding in the dark and damp.

The trick, I think, is to use methods in combination. I've resorted to using copper tape to protect pots and individual plants such as brassicas and squash on the allotment, plus a good watering with anti-slug nematodes when the conditions are right and I can afford it, plus using organic pellets in very specific closed environments where there is no danger of other wildlife ingesting them, plus morning and evening inspections around the garden and allotment when the weather is damp and after rain (when I will despatch the slugs as quickly as possible by snipping them in half with scissors). It's time-consuming, but slightly less stressful than losing all your squash or salad seedlings to a fat, but still hungry slug.

I've collated the methods I've used (some more successfully than others) into the table below. I'd love to know about any other effective ways to remove, deter or eliminate slugs and snails and make this as comprehensive as possible.

The Method	Advantages	Disadvantages
Pellets	Kills slugs and snails	Harmful to other wildlife
	Easy to apply	Requires reapplication
	Inexpensive	Messy corpses
	Effective

This is what happens when a slug ingests a slug pellet: the methiocarb
in the pellet causes the slug to over-produce mucus and it dies of dehydration, 
leaving you with a nasty slimy mess. Any predator that tries to
eat the dying slug may well be poisoned in turn by the methiocarb
in its system.

Beer traps	Kill slugs and snails	Messy corpses to dispose of
	They die happy	Ineffective against large numbers
		Requires maintenance
		Waste of good beer
Other traps, eg, grapefruit halves	Does not kill, pests congregate in grapefruit halves	Live slugs and snails to dispose of
Copper tape	Non-toxic	Does not kill; the pests will go elsewhere
	Environmentally non-invasive	Relatively expensive
	Effective	Risk of trapping pest INSIDE the pot
	Taped pots can be reused

A simple copper collar made out of a section of plastic water bottle
lined with sticky copper tape

Coffee grounds	Does not kill; the pests will go elsewhere	A LOT of coffee grounds needed for more than one or two plants; you will need to befriend local Starbucks or similar
	Environmentally non-invasive – grounds good as mulch	Ineffective against large numbers
Sharp grit, etc		Does not kill; the pests will go elsewhere
		Do you really want your beds full of grit?
		Risk of trapping pests inside the barrier
Torchlight patrols	Non-toxic	Now you have to kill them
	Environmentally non-invasive	Disposal of corpses
		Effectiveness depends on your vigilance
		Morale-draining in face of large-scale invasion
Encouraging or introducing predators: birds, frogs, hedgehogs, geese, etc	Non-toxic	Easier to achieve in a rural environment
	Potentially highly effective	Requires maintenance at least initially
		Potentially expensive outlay (digging out a pond, acquiring geese)
Introducing predators: nematodes	Non-toxic	Not nearly as effective against snails, only slugs
		Expensive
		Requires reapplication

There are around 30 different types of slugs that live in the UK,
only around 4-5 of which will out of choice eat your vegetables.
These are two of the bad guys: the imaginatively-named
black slug, top, and the red slug, above.

Further reading

http://eartheasy.com/grow_nat_slug_cntrl.htm - US-based article on natural methods of curbing or eliminating slugs and snails.

http://urbanvegpatch.blogspot.co.uk/2014/04/a-slug-is-slug-no-matter-how-small.html - some more ideas for getting rid of slugs and snails and a photo which almost makes them look pretty.
http://secret-garden-club.blogspot.co.uk/2013/04/as-soil-warms-up-and-new-spring-growth.html - how to buy and use nematodes as a biological control.
http://www.telegraph.co.uk/gardening/gardeningequipment/8675592/The-war-on-slugs-starts-at-home.html - how to make your own nematode soup (warning: the method is somewhat icky)
http://adlib.everysite.co.uk/adlib/defra/content.aspx?id=178456 - know your slugs: an identification table to UK species.

Keeping pests at bay

Garlic (Solent Wight) on the left, Egyptian walking onions behind, hopefully protecting the Chinese broccoli (kailans) and kohl rabi seedlings. The copper-lined collars prevent slugs and snails from reaching the brassica seedlings.

I planted out these heavily guarded brassica seedlings yesterday. Bitter experience has taught me that they need this level of protection. The copper-lined collars are made from sections of 500ml plastic water bottles trimmed with copper tape around the top and will deter slugs and snails. The metal reacts with the mollusc's mucus when it tries to cross the copper strip and gives it a shock-like sensation.


I've found these home-made copper rings perfectly effective and use them with brassica seedlings, cucurbit seedlings, lettuces, of course, and also globe artichokes when they are first planted out. I can still remember the heartbreak of coming home after an Easter weekend away and finding my globe artichokes, planted out on Maundy Thursday, had vanished. The only clues to their disappearance were a number of long, ribbon-like, shiny trails.


The only drawback really, apart from the need to have as many collars as you have seedlings in the ground at any one time, is that the slug/snail population isn't controlled. In a particularly sluggy year, they will go off to try to find something else to eat that's unprotected. One year I found slugs attacking the beetroot, which is not normally vulnerable. This year, with a wet April with showers interspersed with sunshine, we are on Code Red as far as slugs and snails are concerned.


The second level of protection here is the perimeter planting of various alliums. I have deliberately positioned garlic (pictured here is Solent Wight, with elephant garlic out of shot) and onions around the outside of the raised bed to deter cabbage whitefly. Alliums are often planted with carrots to deter carrot fly, as it is said that the onion smell confuses the carrot fly (and also that the reverse holds true, the carrot smell deters the onion fly who is after an allium snack). 


Here I am hoping that the same principle holds true against whitefly. If this mini-trial proves successful, and the kohl rabi and kailans in the raised bed remain relatively whitefly-free, I will extend it to the main brassica bed, where the cauliflower, broccoli and cavolo nero will be planted later in the summer. Last year, the cavolo nero in particular was horribly infested with whitefly to the point of not being able to harvest it.


Copper tape is available from larger garden centres and from a number of online gardening suppliers. It's well worth searching and shopping around as prices can vary widely. Copper rings are also available but tend to be much more expensive while performing exactly the same function as the homemade rings here. For a copper ring with a larger diameter cut sections from a 2l water bottle.

Clockwise from top left: cut an empty water bottle into sections; take the mid-section and line with copper tape, tucking the ends over the rim to make a neat edge.