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coffee-grounds against slugs and snails

Mulch Barriers to Protect Plants Against Snails and Slugs: Do They Work?

A mulch that not only keeps soil moist and weed free but also repels snails and slugs – would that not be wonderful?

Many approaches promise precisely that and are widely publicized on the internet:

  • coffee grounds
  • sawdust
  • sheep’s wool
  • and more…

Unfortunately, information on the effectiveness of these materials is contradictory.

Not only that, but the descriptions on how to use them differ.

So, I collected as much information as possible and ran tests to validate the statements.

Unfortunately, they showed that many mulching materials fail as slug protection as soon as they get wet.

barrier mulch slugs snails
Is it possible to block the way into the beds?

Which Materials Are Useful and Which Are Not?

The reasoning behind most recommended mulch materials is that slugs and snails do not like to crawl over dry surfaces.

On dry soil, they lose a lot of mucus and, with it, vital moisture.

So, materials that are exceptionally dry should serve as protection.

The second group of materials has particularly sharp edges. These should hurt and harm the slugs, thereby stopping them from proceeding to the plants.

Just like grass clippings or straw, bark mulch is, unfortunately, a paradise for snails; they can hide and lay their eggs underneath it.

You should avoid these materials if slugs and snails are a problem.

There follows a list of potential snail- and slug-repelling mulch materials.

egg-shells against slugs
Eggshells against slugs?

Eggshells

The sharp edges of dried, crushed eggshells should deter slugs and snails.

At least that is the opinion of some people who recommend this home remedy.

Unfortunately, just as many voices claim the opposite.

Some people believe it would be essential to use only the shells of uncooked eggs because cooked eggshells will not be sharp enough.

I conducted a test to find out whether eggshells work against slugs and snails and was somewhat disappointed.

You will find more information here: Eggshells against slugs and snails

sawdust wood shavings slugs
Sawdust as a protective mulch against snails?

Sawdust

Wood shavings and sawdust should work because they are very dry, so slugs and snails do not like to move over them.

This remedy, too, has both advocates and critics.

One significant disadvantage is that shavings lose their deterrent effect in a moist environment and slugs and snails can then use them as a shelter.

You will find more information here: Sawdust and wood shavings against slugs


Slug Control with copper for raised beds, planters & pots

Control slugs with copper using:

  • copper-tape
  • copper-mesh
  • copper-wire.
Slug Repellent Copper Tape Copper Mesh Fence Copper Wire
Check prices on Amazon Check prices on Amazon Check prices on Amazon

Rock Dust

Rock dust/rock flour is extremely dry, so should be useful as a slug barrier.

But again, the problem is that it becomes useless with rain or irrigation.

Rockdust is beneficial for soil health, so it cannot hurt to build protective walls with it.

I also tested the effect of rockdust on slugs, with little success.

Video: Rockdust against slugs and snails


You will find more information here: Rock dust against snails

coffee against slugs and snails
Coffee against slugs?

Coffee Grounds

Another widespread belief is that caffeine is deadly to slugs and snails; it should make them sluggish at a low dose.

What about these claims?

I wanted to know more, so devised a test and recorded on video how snails react when they encounter dried coffee grounds.

The results are slightly disappointing.

You will find more information here: Coffee grounds against slugs

sheeps wool against snails
Sheep’s wool against slugs?

Hair and Wool

A promising mulching agent is untreated sheep’s wool.

In my tests, the wool showed that it successfully deters slugs and snails, at least until the rain comes.

So, the wool could be put to good use in a greenhouse or a cold frame.

Unfortunately, human hair has proved to be ineffective.

You will find more information here: Sheep’s wool against snails


Slug Control for larger areas and garden beds

To protect larger areas use:

  • slug fences
  • sheep wool pellets.
Slug Fence Set: Small Slug Fence Set: For 6m² Sheep Wool Pellets
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sea shell grit sand against slugs snails
Do seashells protect plants against slugs?

Seashells

Crushed seashells should be so sharp-edged that snails will not want to crawl over them.

It might make sense, therefore, to lay crushed seashells out on the paths around beds, for example, or to use them to build up small protective walls around endangered plants and beds.

But even this remedy is very controversial. I have not tested it yet.

You will find more information here: Crushed seashells against snails

lime against slugs snails
Garden lime against snails?

Lime

Standard garden lime should also act as a deterrent against snails.

Sometimes quicklime is recommended; it is said to be an insurmountable barrier due to its corrosive effect on snails.

From time to time, even the toxic calcium cyanamide is brought into the discussion.

I have not tested lime yet, and I do not recommend it because there are better alternatives.

You will find more information here: Lime against slugs and snails

ash agsint slugs and snails
Do slugs cross ash?

Ash

Ash follows the same logic as lime.

It is very dry and therefore absorbs mucus, so snails should avoid crawling over it.

Again, opinions on its efficiency differ widely.

Since ash is sometimes contaminated with heavy metals, you do not want to sprinkle it on your vegetable garden.

As I am always skeptical, I once again devised a practical test.

The result was that dry ash deters snails and tiny slugs, but not bigger ones.

You will find more information here: Ash against snails

salt kitchen not garden
Salt against slugs?

Salt

One of the worst home remedies recommended against slugs and snails is salt.

It is true that snails do not crawl over salt but sprinkling it around the garden is very negligent.

Salt harms not only slugs and snails, but also plants and beneficial animals.

If the soil becomes acidified, you should compensate with lime, otherwise most living beings will not be able to live there anymore.

So, I recommend you steer clear of this remedy.

You will find more information here: Salt against slugs and snails

diatomaceous earth
Is diatomaceous earth the solution against slugs?

Diatomaceous Earth

Also questionable is the application diatomaceous earth.

This fine dust of fossil algae is lethal for many animals, mainly insects.

Even people who inhale diatomaceous earth can get sick.

I therefore advise against its usage in the garden.

You will find more information here: Diatomaceous earth against slugs and snails

mint dried leaves tea
Dried mint leaves against slugs?

Dried Mint Leaves

A secret weapon might be dried mint leaves.

Since I was interested, I tested them myself.

You can see the results in the following time-lapse recording.

Video: Mint Against Slugs and Snails

Surprisingly, the test showed that the mint leaves repelled most slugs and snails.

Quite a lot of the slugs and all of the snails turned around after coming into contact with the mint leaves.

Further testing is needed to find out if this method also works when the mint leaves are wet.

If you watch the video closely, it seems as if the smell alone could repel them.

barriers mulch slugs snails deterring repelling
Sheep’s wool and mint are the winners.

Conclusion

In my opinion, only sheep’s wool can be recommended, since it withstands at least light moisture.

Mint leaves may work, too.

However, most mulch materials are not efficient enough even when dry.

Due to moisture, they immediately become ineffective and are therefore not helpful as slug control.

When it is dry, most snails are not very active anyway. Protection is needed most when conditions are damp and moist.

The use of diatomaceous earth and salt in the garden is best avoided entirely. Their side effects are too dangerous.

The above list is of course not exhaustive, and I am still looking for more resources.

It would be awesome to discover a mulch against snails that is simple to apply and at best can even be made at home.

For every tip in this direction, I am very grateful!


Slug Control for single plants

To protect single plants use for example:

  • plant covers
  • garden cloches
  • slug collars.
Protective Plant Covers Garden Cloches Slug Collars
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Last update: July 15, 2018


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7 thoughts to “Mulch Barriers to Protect Plants Against Snails and Slugs: Do They Work?”

  1. I tried wood ashes, once, on clay soil. Figuring their effectiveness would diminish after the first rain, I covered the ashes with black plastic. I think I got good slug protection. However, my tomato plants grew six feet tall before blooming and didn’t produce much fruit in my northern location with a short growing season.

  2. I have recently used sheep’s fleece which has been fairly effective although each plant needs a collar of it, also wee sluglets still come up inside the collar. We also put empty bottles which have pasted on labels near the vegetables and tomato plants as the slugs and snails feast on the labels which presumably have been stuck on with a ‘tasty’ glue!!! Also corrugated cardboard seems to also be equally attractive!

  3. I find it somewhat humorous that diatomaceous earth was avoided by the author because “Even people who inhale diatomaceous earth can get sick.” Yes, inhaling any fine dust can make a person ‘sick’ in the same way. Inhaling fine dust of any kind isn’t good for people’s lungs, but there’s nothing poisonous about diatomaceous earth, and it can’t make you sick like a poison does. I’m very disappointed that the author didn’t try it because they were fearful they might inhale some. Kind of silly considering all the other dusts people are exposed to on a regular basis.
    Ever spray paint? You’ve inhaled the fumes. A little won’t really hurt you, but you should do it outside so you don’t inhale a whole lot – but you’ll still inhale some. Cool how we don’t worry about it, even though it’s really dangerous. Same thing. Use caution and common sense. Don’t apply diatomaceous earth when it’s windy, for example. BTW – ‘dusting’ large animals (dogs, goats, etc.) with diatomaceous earth will kill fleas and lice. And again, as long as you don’t make a huge dust cloud while doing it, it’s completely safe for the animals and you.

  4. As I started reading, I noticed diatomaceous earth was on the list at the top, and I was eager to find out how well it compared to the others. Imagine my surprise when the author DIDN’T EVEN TRY IT!!!! (Why even mention it then, and put it on the list!?!) And their reason for not trying it? Because “Even people who inhale diatomaceous earth can get sick.” What is that supposed to mean? “EVEN people … can get sick.” Diatomaceous earth doesn’t make snails, slugs, and other creepy crawlies “get sick” at all!! It scratches their outer bodies, making them dehydrate and die. BIG difference! Because of how it works people shouldn’t inhale the dust, but handling it is just as safe as handling dirt! (Dirt is actually more dangerous because of pathogens that live in it!) People and animals even eat diatomaceous earth – it’s used as a ‘flowing agent’ in some foods, and the FDA doesn’t require it to be placed on the label! Seriously? “EVEN people … can get sick.” ! ? ! ?

    Obviously you should avoid making a dust cloud while using it, which should be avoided with ANY powder used for ANY reason. Our lungs aren’t made for breathing dust. I wonder if the author would have avoided using baby powder if that was something people used for snails & slugs, or if they would have avoided it, saying “EVEN people who inhale baby powder can get sick.” Diatomaceous earth may be an irritant to human lungs, but at least it doesn’t cause cancer like talc does – you know – baby powder?

  5. People who minimize the real risks of using diatomacous earth have apparently not schooled themselves on the facts. See “Health hazards due to the inhalation of amorphous silica” https://www.ncbi.nlm.nih.gov/pubmed/11876495
    “People and other mammals should never use the coarse, crystalline form of diatomaceous earth sold for use in swimming pool filters or as insecticides, or sources of diatomaceous earth contaminated with toxins like arsenic and the metal toxins. If inhaled, the crystalline form can cause a disabling lung disease called silicosis”
    https://www.westonaprice.org/health-topics/environmental-toxins/mad-as-a-hatter/

    Not only that, can anyone justify its deadly effects on bees and other pollinators, when their very survival (and ours, if crops are not pollinated) is already threatened?

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