Instructables
Picture of Electric Garden Slug Fence
Slugs will ruin a vegetable garden pretty fast unless some serious means of taking care of them is implemented.  The electric fence has proven to be pretty well 100% effective in my experiments to date.  The fence consists of two runs of wires spaced about 3/4 inch apart running around the perimeter of the raised bed - one wire is connected to the +ve terminal and the other to the -ve terminal of a battery. An electric current will flow through the slug if it makes contact with both wires at the same time. The resulting "shock" with usually cause the slug to turn back. 

I've been using a 9-volt battery as the power source, the battery  lasts the whole growing season but the voltage drops to 5 volts or so by the end of the season (my measurements). It's a good idea to check the volage once in a while to make sure the battery is still providing enough voltage (corrosion can be a problem at the battery connectors).  A few years ago when setting up a new fence I didn't have a 9-volt battery connector so I used a multi-battery  AA holder that I had on hand.  The combined series connection of batteries gave 12 volts.  This turned out to be a bad idea as the 12 volts would more often than not kill the slugs rather than just turn them away. 

The nice thing about the slug fence is that it is on duty 24-7, many other slug control methods require some kind of regular checking or resupplying.  Also, no dangerous chemicals to worry about with this setup.

My first electric fence was mounted on a low "raised" bed garden.  It was effective until the vegetation in the garden grew high enough to bend over and touch the ground - this gave the slugs the bridge they needed to reach the main feast.

The video below demonstrates how a slug typically reacts when attempting to cross the fence.  It is interesting to notice from the video that once the slug was "shocked" a number of times (by making contact with both wires) it was then conditioned to react the same way when touching just one wire (no current flow possible through the slug).
 
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I watched the video. I have a bean garden and the slugs are terrible when it rains... i applaud you!. (also the sound effects made me laugh )

nlinventor (author)  jon.blymiller1 month ago

Thanks jon... yeah around here they do a lot of damage throughout the growing season.

bcavaciuti Reiff5 months ago

slugs do loads of harm...they eat plants so make holes in the leaves, fruits and stems of your plants causing them to either die, cause scars or allow rot in therefore spoiling the food which you put your time and money into.

heartwork5 months ago

This is one of the articles which motivated me to do my own electric slug fence project. Although I do not have raised beds, I made my fence on the ground, using some old planks - and it works. Number of slugs on my salad after installing it = 0. I made a blog entry about it (hope it is not intrusive): http://spacepetuniareview.blogspot.com/2014/05/slug-wars-chapter-1-making-diy-electric.html

Cheers!

gabigirlhs6 months ago
Just made two....let the growing season begin!!

One question to you all..... how do YOU test your snail fence? ???
nlinventor (author)  gabigirlhs6 months ago

Other than what I did for the video (placing slugs near the fence) you could use a simple multi-meter (VOM) set to voltage. Measure the voltage between the two wires anywhere along the run (not at the battery terminals only). I'm thinking that anything above 4 volts should work.

I tried that with a battery tester. Do I have some wrong thinking going on there? I thought that would work. It didn't show anything. I ended up doing the tongue test. That did work. ;-) I was hoping to find another way though.
nlinventor (author)  gabigirlhs6 months ago

Wonder if you tried the tester at the battery terminals? If it showed voltage there then there's a good chance that you need to make better contact between your tester and the wires by just pushing hard against the wires with the test pins/clips (I'm basing this on the positive results of your tongue test).

maximzodal6 months ago

I like it. Simple, and effective. Very good information.

maximzodal6 months ago

This guy got tired of deer eating his garden every night and hooked a live 110v wire about three feet high around the perimeter. Yeah, I know, dangerous as hell. I'm not advocating this. Early every evening he would plug it in at the house and it worked, no deer. So, one night he forgot to plug it in until right before going to bed. Next morning he found three deer inside the garden.

confu2 years ago
A few days ago I thought about a modified version of this, for teaching a cat that enjoys pissing at our terrace door a lesson.
There are some metal stairs outside the door on which the cat must be standing while "marking" the door.
I will try to connect one pole of the 9V battery to the metal grid and make kinda spiral of wire that sticks to the door and connect it to the other pole.
I´m curious ;) Evil cat!
pcooper2 confu1 year ago
Your idea has a very low probability of working. There was an episode of the "Mythbusters" television show wherein they tested the story of a railway worker being electrocuted while urinating on the third rail. They used a dummy rigged to emit a stream of salt water to simulate a urine stream. High-speed photography revealed that the "urine" stream was breaking into droplets as it fell, and thus the electric circuit was not being completed.

I agree with finton, I've seen the effects of peeing on an electric fence and it was 'jolting'. Also on a small gas engine spark plug.

finton pcooper210 months ago
And yet the idea worked fine when I peed, in the dark, on a farm's electric fence many years ago...
Create a Walcroft - Walton voltage multiplier circuit, from a small AC transformer - ramp it up to a few thousand volts DC with a capacitor on it.

This will solve the problem
Don't you mean "Cockcroft-Walton" ... ?
darkisland517 months ago

A question: Where do get the battery connectors? I can imagine pirating an old flashlight or some other dollar store-type item. If you update this instructable, could you add some pictures along this line, and additional instructions?

nlinventor (author)  darkisland517 months ago

darkisland51 - 9-volt battery connectors are available from electronics supply stores such as Radio Shack and The Source.

aje1272 years ago
Brilliant. But why wouldn't you want to just Kill the slugs. I hate those slimy things.
hesspet aje1272 years ago
Using chemicals is a bad idea. It's the best way to get more snails. If the snails die by the chemical they throw away their eggs (they have a lot of them in their body) and for one dead snail u will get 100 after some weeks. Chemicals are a woderfull sample of how to fool consuments.

Btw: Beer has the same effect. Snails you do not have in your garden like the beer and on the way to the beer trap they have sex. Same result. So the electric fence is a very good solution.
Metaldehyde works quite well on snails and slugs. They don't get far after ingesting it and have no opportunity to lay eggs. It's been used for over 80 years with great success and is the active ingredient in most snail and slug baits. Moreover, when exposed to sun and water, it decomposes into harmless components.
hesspet pcooper27 months ago

Inside the chemicals is an attractant. This is the fooling (or better , the bad idea). If you have some snails in your garden use such chemicals and your garden is full of snails after the usage (beer is also very attractive for snails). Not all killed by the poison of metaldehyde. So you need more of the poison, you have more snails and so on....This is the fooling of the industry which produces the baits since 80 years. The metaldehyde is not the problem, it works :-) it's the attractant.

Since the day I learned this, our garden was full of snails. Then we stopped using the poison and spend may evenings collecting snails. And we add some mechanical barrieres and a sand way around the garden and sort of electrical fences. No more problematic snail population.

Then we were in holidays and a friend live for some weeks in our house and he used again the poison, cause he found some snails. No problem pick them up and remove them, that's what we do, he use again slug bait). Argggggggg.... snails everywhere. So again weeks of collecting of those red salad killers :-) to free the garden.

BTW: There is a second problem: The metaldehyde kill all snails. There are a lot of snails around which does not eat you garden plants, they eat rotten leaves and similar things. They are also killed.



nlinventor (author)  pcooper21 year ago
pcoper2 - It is best not to let the slugs get in the raised bed at all. The fence, as described, has been pretty 100% effective as mentioned. No chemicals of any sort to worry about. Also, as you mentioned, metaldenhyde decomposes with sun and water and would therefore require upkeep. With the electric fence you can go away for weeks and not have to worry (about slugs that is).
My comment wasn't intended to be critical of the electric slug fence concept. Indeed, I think it's a good idea. However, there are people commenting here who apparently have a morbid fear of using any kinds of chemicals in their gardens, when some chemicals are quite safe and do not create persistent pollution of the soil.
nlinventor (author)  aje1272 years ago
aje127 - Just too many to kill around here. Best thing is to redirect them, hopefully to weeds :).
I have been trying to find an effective deterrent for slugs without pouring more chemicals into the ground. Will definitely be trying this out in the spring. Going to try one bed with 9v and one with 12v to see if I can see a marked difference in the weed population around each box.
Use any snail and slug bait whose active ingredient is metaldehyde. Metaldehyde decomposes into harmless components in the environment and it is extremely effective in controlling snails and slugs.
nlinventor (author)  tandync2 years ago
tandync - should be interesting :)
aje127 aje1272 years ago
Well actually I was thinking about upping the voltage...a bit. instead of 'training' them, just electrocute them and be done with it.
gabigirlhs7 months ago

I am going to try my first slug fence very soon, I love the idea....I have a question though...I have seen versions with "electric fence" such as ones used for containing animals. Has anyone tried this??....this electric fence version with plastic fencing with wiring through it which I have seen is sold online. The instructions are such that the ends are not allowed to touch one another. Otherwise it is basically installed the same. I was hoping to make mine myself without buying the parts like with your system here. But ... I am just keeping my options open and wanted to know what you think about this plastic fence system. Thanks

nlinventor (author)  gabigirlhs7 months ago
Have never worked with animal type electric fences but from what I know they are high-voltage low-current setups. That means you or anyone else working around the fence would get a major jolt if you make contact. I assume the shock is not dangerous because of the low current feature (unless you have a pacemaker maybe). But this arrangement is not really suitable for slug control as I described it. My system is powered by a 9-volt battery which is pretty safe to work around under most situations.

Yes...I realize that with the 9v. And yes....the fences would normally jolt through a high voltage...however this system is also set up with the 9-volt battery just as yours is.... My thought was....and I know this is silly...but the plastic electric fences lies flat on the bed and is less obvious. Another thing they showed was a copper band set up with the 9v battery, same principle but certainly more expensive with copper prices. The copper band is taped on which surely does not hold for more than one or two seasons unless everything gets dismounted over the winter period.

How is your system with getting wet or being rained on??? The electric plastic fence type recommends putting a border board over it to protect it from getting too wet and therefore losing its umpf. By us (as I assume it is everywhere), when it rains the slugs multiply like crazy!! I got rid of my garden just because of them but am thinking of making a small raised bed with the hopes of zapping them in the other directions. We are in the midst of designing our own DIY raised beds for my mother in law and I want to get hers slug free for her....and then maybe try a few salad beds for me and my family without having to feed those slimy creatures too ;-)

nlinventor (author)  gabigirlhs7 months ago

gabigirlhs can you send me a url with the info on the system you are referring to. No problem when my system is wet as the spacing between the conductors, even with wet wood, keeps the electrical resistance high enough to prevent unduly draining the battery. Battery lasts all season and I'm in a wet area.

ahurst28 months ago
Wow! Great solution!
nlinventor (author)  ahurst28 months ago

Thanks ahurst2 - one point I didn't stress or even mention is that this method of controlling slugs is actually the most humane that I am aware of. If I were a slug I'd take a little tingle rather than die in agony from poison or salt. Other methods that are out there just don't work well enough to make them practical - at least that is my experience and opinion.

maybe make a beer trap with and electric fence..................;)
Great i'ble! Am planning to do this now - especially as I discovered about 20 slugs massacring my seedlings this morning after a rain shower last night. It's hard to have sympathy when they eat the whole plant and leave nothing to grow.
Anyway, my question was: How long do you think the wire could be? I have 4 raised beds together, so was wondering if I could put a perimeter fence around the lot (about 24 foot by 8 as they're 6x8 each) or whether I'd have to do them individually.
Many thanks, Duncan
nlinventor (author)  duncangallimore1 year ago
Thanks - no real limit on the wire length as the standby current flow is so small. The voltage will remain the same all along the wire. When a slug makes contact with both wires there will be a voltage drop while in contact but after that back to standby voltage (approximately 9 volts). In my situation this is an essential feature for my raised bed - just like you, my garden would not have a chance otherwise. Good luck!
iTixle1 year ago
Do it with a MOT ;)
Yeah that would cook them instantly.
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