Their borders act as a block so slugs and snails cannot enter the beds.
The special double-bent edge prevents the creatures from moving to the beds.
When trying to battle their way over the edge, the animals fail and sometimes even fall, disoriented.
At least, this is what the slug fence manufacturers maintain.
But how effective are these fences in practice?
Snail and slug fence long-term test site: their favorite food under guard.
Slug Fence Test
To put slug fences to the test quickly, I came up with a special experimental set-up.
Then I grabbed some freshly collected snails and slugs and conducted a practice test with them.
I recorded the results on video (see below).
I did not do the test with a metal slug fence, but with the plastic version.
Nevertheless, the results apply equally to all slug fences based on the double-bent edge principle.
On YouTube, you can find a video describing the installation of the plastic fence.
If you follow each step in this video, you get a fence with an edge, which is bent twice in 90-degree angles.
Video: Installation of a Plastic Slug Fence
Test Implementation
For the experiment, I constructed a small dead end with the slug fence and put the snails in the middle.
Then I recorded around 32 minutes of video (with time-lapse) and watched closely what happened when the slugs and snails tried to climb over the fence.
(Since my goal is to find ways to control slugs and snails without making them suffer, I hope this sort of animal experiment is okay. The slugs and snails were treated well and were released afterwards. The Spanish slugs were resettled far away. I am, in fact, against animal testing.)
What I wanted to find out was how they would react to the contact with the bent edge and whether they would manage to overcome it.
This experiment works particularly well with transparent slug fences made of plastic.
This makes it possible to see on the video how the slugs and snails react when they encounter the edge.
Snail Fence Test No.1: 90-Degree Edge
During the construction, I kept to the above video and the instructions on how to build the fence.
However, I constructed the fence in the opposite way: namely, with corners on the inside instead of on the outside, so that the slugs, if the fence works, cannot come out.
You can see the result of the first attempt here:
Video: Snail Fence Test # 1
This first attempt failed. Most slugs and snails did not want to crawl over the fence – I do not know why.
Maybe the fence was still too fresh and smelled unfamiliar.
Impressively, however, a leopard slug was quick to make it to the other side; this indicates the weaknesses that come with this style of edge.
This first experiment shows how easily slugs can ‘flit’ over the 90-degree edge.
A fence with this sort of edge has therefore proved to be ineffective against slugs.
Slug Fence Test No.2: 45-Degree Edge
Since the first attempt failed, I made a second attempt the next day.
This time, I bent the edge further inward, as is the case with the original metal slug fence.
Now the edge had an angle of about 45 degrees.
This time, the slugs were much more motivated to accept the challenge.
Video: Snail Fence Test # 2
With this slight change, the fence successfully fended off most slugs and snails.
Only one tiny snail managed to climb over the top of the fence, and two slugs squeezed through underneath.
The winner was a little grove snail.
Snails are obviously better climbers than those of the same species without a shell.
Slugs usually stay near the ground. Maybe that’s why they cannot climb as well as snails that also live on trees.
The 90-degree edge failed, and the 45-degree edge successfully prevented all slugs from crossing the fence.
The tapering edge has – to my delight – managed, without any violence, to ward off all slugs.
Many slugs have tried it, but all have failed. They turned around again or fell off the edge.
Only a small snail could do it. But since these snails pose no danger to the plants, there is no reason to be concerned.
This makes the slug fence an environmentally friendly alternative.
So, no slug has to be killed to harvest vegetables.
Practical Experience
Metal fences have proved to be very effective in practice.
Metal slug fences come with corner connectors.
But you should be careful that no plants grow over the fence; this could then be used by the slugs as a shortcut.
You will find more information about construction and handling here: Slug fence manual
Unfortunately, there is a small problem with plastic fences: in contrast to the metal variety, they have no extra corner pieces, so this creates a vulnerability.
If the edges are only bent by 90 degrees, the corners can be trimmed well and bent without gaps.
This is well described and shown in the above video.
But if you want to bend the edge by 45 degrees, a small gap is created in the corners, which slugs could find.
So, you either need to improvise or accept that some slugs can get inside through these weak points.
With a little manual skill, you can build similar corner pieces, as for the galvanized slug fences.
If you have any experiences to share, I would be happy to read your comments below.
The test indicates that the mechanical defense by the 45-degree edge works well.
However, you should keep an eye on slug fences with a 90-degree edge.
Both metal and plastic fences work well, but you will have a problem with the corners of plastic fences.
If you want to be on the safe side, you are probably better choosing a metal fence.
Although rustproof metal fences are not cheap, they are well worth the cost, as they will last for many, many years.
The fences provide plant protection that works without poison or violence.
Snails are gently warded off. No snail has to die or be killed, and the use of slug pellets is unnecessary.
Nevertheless, one can effectively protect a large area in the garden.
So, without a guilty conscience, I can warmly recommend the purchase of a slug fence to anyone who wishes to defend vegetables and flowers without violence.
Thank you so much for going to so much effort to show us how the slug fence works. I don’t have a slug problem but I do have some hungry snails. I was researching to see if the broken sea shells I can gather nearby are effective when crushed and scattered to form a barrier. Lovely site. No need to reply. Em
Thank You for taking the Thyme to help me be more kind in the Garden — I refuse to kill slugs — they are Creatures also…. I deeply appreciate the effort you have taken to discover and Teach Compassionate Gardening techniques! Thanks! I will be putting your Wisdom to work!
Thanks so much for this article. I found it to be very informative. I have taken a laissez faire attitude to slugs because I realized years ago that I was torturing the poor creatures with slug bait. However, at my current home, there is an army of them, huge and happy…mainly attacking my peppers and greens. I had no idea there were slug fences until I read your article. I will definitely be seeking one next spring.
Thank you so much for going to so much effort to show us how the slug fence works. I don’t have a slug problem but I do have some hungry snails. I was researching to see if the broken sea shells I can gather nearby are effective when crushed and scattered to form a barrier. Lovely site. No need to reply. Em
Thanks – very helpful!
Thank you so much-extremely useful. At last a way to deal with slugs!
Thank You for taking the Thyme to help me be more kind in the Garden — I refuse to kill slugs — they are Creatures also…. I deeply appreciate the effort you have taken to discover and Teach Compassionate Gardening techniques!
Thanks! I will be putting your Wisdom to work!
Loved the time lapse videos. Really interesting. Thank you
Thanks for all your hard work in writing this! Very helpful 🙂
Thanks so much for this article. I found it to be very informative. I have taken a laissez faire attitude to slugs because I realized years ago that I was torturing the poor creatures with slug bait. However, at my current home, there is an army of them, huge and happy…mainly attacking my peppers and greens. I had no idea there were slug fences until I read your article. I will definitely be seeking one next spring.
brilliant helpful thank you