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
- 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.
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.
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
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
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
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
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
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
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 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
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
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
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.
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!