Slug Treatments that Really Work!


20150716IOver the last two days, I presented two slug treatments of varying effectiveness. The eggshell barrier treatment does not work at all. The beer slug trap does work to a certain extent, but is not very effective. Here are other treatments against slugs along with an assessment of their effectiveness.

Diatomaceous Earth

20150716ATreatment: Surround the plant with a circle of diatomaceous earth (a white powder derived from fossilized algae).

Effective: Slugs seems to hate diatomaceous earth and will avoid crossing a barrier made of it unless very hungry. The theory I keep hearing is the sharp particles of diatomaceous cut the slug’s delicate skin, leading to its death. This is nonsense, of course. First, slugs have a very tough epidermis, not easily scratched, and secondly, they give off a slimy mucus to allow them to travel over the roughest, sharpest surfaces, so ought to be able to travel readily over diatomaceous earth. The proof of the pudding is that, if they are forced to cross diatomaceous earth, slugs are in no way damaged by their passage. The real reason they avoid this product remains a mystery… but they do!

Downside: The barrier must be replaced each time it rains.

Wood Ashes

Treatment: Surround the plant with a circle of wood ashes.

Effective: Again, slugs have so far refused to answer questions as to why they avoid wood ashes, so it is not known if they avoid them because they are so alkaline (pH of 10 to 12!), whether they don’t like their texture, or if some other factor is involved. Whatever the reason, slugs don’t seem to appreciate them,

Downside: The barrier must be replaced after each rain. Also, if you apply too many ashes too often they can render the soil too alkaline for most plants.

Coffee grounds

Treatment: Surround the plant with a circle of coffee grounds.

Ineffective: Slugs will cross a barrier of coffee grounds barrier as it if weren’t there. Totally ineffective.

Copper Barrier

20150716BTreatment: Surround the plant with copper tape or netting. You can also fix copper tape or netting to the sides of pots or raised beds to prevent slugs from climbing up.

Effective: It is often said that slugs receive a small electric shock when they touch a copper barrier. Whether that’s true or if some other factor is the cause is not known, but it has been clearly demonstrated that slugs will generally avoid crossing a copper barrier.

Downsides: Copper in any form can be quite expensive. Also, when it rains, copper barriers placed on the ground are often partially covered in soil, in which case the slugs will not hesitate to cross them.

Slug Bait Containing Metaldehyde

Treatment: apply pellets containing metaldehyde to the ground or pour them into a trap with openings only large enough for slugs.

Effective: Slugs eat the poison and die.

Downsides: Product not recommended! This product is highly toxic to pets and wildlife and even (to a lesser extent) to children. Most suppliers add Bitrex to their pellets, a very bitter product that slugs don’t notice, but that mammals quickly spit out, thus reducing the risk of accidental poisoning. Birds, however, generally ignore Bitrex, so can still be poisoned. If this product is used, it’s best to place this type of bait in a trap or under a length of board, away from curious animals. Even though this product is still available, few experts now recommend it for domestic use. It has been widely replaced by slug bait containing iron phosphate (described immediately below). Other caveat, granules exposed to rain decompose and have to be replaced.

Slug Bait Containing Iron

20150716CTreatment: apply pellets containing iron phosphate or sodium ferric EDTA (iron in a sodium EDTA chelate) to the ground or pour them into a trap with openings only large enough for slugs.

Effective: When slugs eat iron, they stop eating immediately, then die of dehydration three to six days later. The two products mentioned as effective with slugs as metaldehyde baits, but are non-toxic to other animals (mammals, birds, fish, insects, microbes, etc.). Moreover, they also act as fertilizers to a certain degree. Both seem to be accepted in organic gardening.

Downsides: The granules decompose when exposed to rain. Suggestion: place them under a board or an inverted bowl to protect them from the elements. Also, if you apply iron-rich year after year in the same place, excess iron can build up in the soil and that will have negative effects on plant growth.

Watering in the Morning

20150716HTreatment: water plants in the morning rather than late afternoon or evening.

Effective: The damage by slugs is greatly reduced when plants are watered in the morning rather than late in the afternoon or in the evening: often by up to 80%! Why? When you water in the evening, the soil remains damp all night and slugs, who are most active at night, just love moist conditions. By watering in the morning though, when slugs are not active, your plants will receive the water they need, but the soil has time to dry out before nightfall and that discourages slugs. Note too that watering in the evening also tends to also increase plant diseases. Avoid watering plants in the evening and you’ll help solve both problems.

Household Ammonia

20150716JTreatment: Spray or water affected plants with a solution of 1 part household ammonia (NH₃) to 6 parts water. Repeat weekly as needed.

Effective: Ammonia is toxic to slugs, but little else in the garden, at least not when properly diluted (it’s very alkaline and, at full strength, may burn the foliage of delicate plants). It’s also a good source of nitrogen for plant growth. This treatment seems most effective on young slugs when they hatch in the spring.

Table Salt

20150716KTreatment: sprinkle ordinary table salt on slugs

Somewhat effective: Even a grain or two of salt causes slugs to start to dehydrate. Apply just a bit more and they will be killed. However…

Downside: Salt is hard to apply, as slugs are not always out in the open on a flat surface where you can reach them with a salt shaker. And you have to apply it directly to the pest, whereas most slugs are pretty much hidden from view. Finally and even more importantly, salt is toxic to plants too and it is almost impossible to apply so it only touches the slugs. Most of it ends up on the ground, contaminating the soil.

Hand picking


You’re allowed to wear gloves while hand picking.

Treatment: Harvest  slugs in the morning or after a rain… even at night with a flashlight.

Effective to somewhat effective: To make slugs easier to find, leave a piece of board, a half grapefruit or an inverted clay pot on the ground: slugs readily hide in the shade near their favorite plants during the day, so you can just lift the “trap” and collect them. When they’re in hand, deposit them in soapy water or use any other method you desire to dispatch them.

Downside: The effectiveness of this method largely depends on your conditions. If slugs are very localized, hand-picking can seriously reduce the population. If there are slugs everywhere, you won’t likely make much of a dint in the population.


20150716ETreatment: release the ducks in the garden, especially early morning when slugs are still active.

Effective: ducks are very attracted to slugs, seeming to prefer them over almost anything else. In Germany you can actually rent ducks for slug control.

Downside: Ducks pull up and eat young seedlings and can also crush plants by accident. It is best to keep them out of the garden in the spring until the plants are well established. Or, release them at the end of winter, before planting, to clean up before planting starts.

Encourage Slug Predators


Ground beetles, often seen in our gardens, are major slug predators.

Treatment: Create an environment that is conducive to slug predators.

Effective: Provide an environment for wildlife, including hiding places, a bit of water, a wide range of plants, and varied environments to encourage slug predators such as snakes, frogs, toads, fireflies, beetles, birds and shrews. And above all, learn to tolerate the presence of these predators. You don’t have to hug a garter snake or kiss a frog: just learn to let them be.

Downside: Some slug predators are less desirable in the garden, among them raccoons and skunks.

Slug-Resistant Plants


Hostas with thick leaves repel slugs.

Treatment: Replace the plants subject to slug damage by species that slugs dislike.

Top tip! This truly solves the slug problem once and for all! Once you get rid of slug magnets like thin-leaved hostas and leaf lettuce, the slug population will start to drop. And since the few slugs that remain are no longer eating your plants (because they don’t like the plants you’re now growing), but instead actively help to decompose dead vegetation, which is theoretically their true role in nature, do you even care if they’re still there? After all, detritus-eating slugs are no longer your enemies, but now your friends!

This is the number one slug control method for truly laidback gardeners, the secret to gardening in harmony with a former enemy. Sometimes gardening is so simple!

Here is a list of slug-resistant plants… and also a list of plants that you should avoid: the ones that attract slugs to the garden.

Trapping Slugs with Beer: Myth or Reality?


In yesterday’s blog20150715A, I explained why an anti-slug barrier made up of crushed eggshells is not effective. I received plenty of flack over that blog (you can’t attack a popular gardening myth with expecting a few angry responses!), but also a lot of questions about slugs, the most popular one being about whether the famous “slug beer trap” works or not. So let’s make it today’s subject.

Is the Slug Beer Trap a Myth?

First, for the thirteen gardeners on the planet who have not heard that you can attract slugs with beer, a bit of an explanation.

20150715BA slug beer trap is a snap to prepare. You just insert a small dish or bowl into the ground and pour some beer in. Any beer will do, even non-alcoholic beer. Slugs, attracted by the smell of malt, are supposed to fall into the dish and drown. Moreover, if you try it, you will indeed find a few drowned slugs marinating in the beer the next morning. So, in principle, it seems to work.

But the time-lapse video above reveals what really happens. Most slugs that visit the trap are content to drink some beer and then continue on their way without any negative consequence. Some even slide right on down into the trap, wallow in the beer then climb back out, apparently very satisfied with their night of drinking. Others (a small minority) also descend into the trap, but don’t leave: they drown and they’re the ones you find belly up the next day. (Nobody knows why some slugs drown while the majority were are uninjured: that remains a mystery).

Another problem: the odor of malt attracts slugs from afar and therefore actually increases the population of slugs nearby and damages to leaves increases. It’s like a sip or two of beer gives the slug hordes the munchies. Therefore plants near the trap actually suffer more damage than plants located far from the trap. In other words, the slug beer trap, when used as usually recommended, does not protect your plants and can even result in even worse damage.

However, there is a method that ensures a beer trap really does reduce the damage caused by slugs. Don’t put the slug beer traps out in your own garden, but instead recommend the method to your neighbor. He’ll try it, be satisfied with the few slugs that drown in the traps, and attract all the slugs in the neighborhood to his garden rather then yours.

O.K., that was kind of underhanded. So let’s be more magnanimous. Place the trap in your own garden, but as far as possible from the plants subject to slug damage, such as vegetables and hostas. This will draw slugs into areas where their leaf eating is not a problem. Clean and top up the trap every few days and you should see your slug population decrease, especially over time.

Tomorrow I’ll do a quick summary of other methods for slug control… and some work very well!

Warning: Eggshells Actually ATTRACT Slugs


This is a repeat, somewhat updated, of a tip covered last year. If you’ve already read it, sorry, but I received several questions on the subject lately and figured it was worthwhile repeating.

20150714DA very popular gardening myth claims that coarsely crushed eggshells are very sharp and that slugs would tear their bodies open trying to cross them. Therefore, by surrounding a plant susceptible to slug damage with a ring of eggshells, you can protect it, because no slug would dare try to cross such a barrier.

In reality, however, the slugs secrete “slime” (mucus) precisely to protect against cuts on rough surfaces. This slime is so efficient they can even cross shards of glass without any damage. Lots of studies have been made about slugs and eggshell barriers and the conclusion is clear: slugs will cross an eggshell barrier as if it weren’t there and without suffering any damage whatsoever.

Until recently, though, it was simply thought that eggshell barriers were not effective. But it’s worse then that. Eggshells, unless thoroughly cleaned to remove the inner membrane and rinsed to get rid of any remaining albumin (egg white), give off an odor that will actually attracts slugs! So “eggshell barriers” are not only ineffective, they actually make things worse.

I highly recommend you visit this website: It’s an excellent source of slug info. Here are some photos from the site I’ve used to illustrate the situation. I’ve added arrows to make things clearer.


Set-up: 2 lettuce leaves are placed on the ground at night.

After about an hour:

20150714AA first slug arrives at the egg shell “barrier” and starts to investigate.

About 45 minutes later:

20150714BSeveral slugs have located the leaf surrounded by shells and are starting to chow down. They have not yet found the unprotected leaf.

The next morning


The “protected” leaf has entirely disappeared. The leaf not surrounded by shells is in better shape, but has also suffered damage.

Another Garden Myth Debunked… But Many More to Go!

The information above is not new: experts have been telling gardeners for decades that eggshell barriers don’t protect plants, but gardeners seem to prefer believing in myths rather than facing reality.

Here’s my warning for gardeners everywhere: just because “everyone says it’s true” doesn’t mean it really is true! If in doubt about a gardening technique, check with a reputable authority to make sure it really is effective.