Electric Garden Slug Fence




Introduction: Electric Garden Slug Fence

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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).

Step 1: The Video Demonstrates the Effectiveness of the Fence

But occasionally an innocent worm will get zapped while trying to cross the fence... 

Step 2: Prepare the Raised Bed Soil and Frame for Planting and Wiring

Tips to help you have a successful growing season:
  • remove old growth and weeds from the raised bed
  • amend the soil as required by adding compost, ph adjustments, and so on
  • DO NOT add homemade compost unless you are absolutely sure it is slug free
  • check around the perimeter of the wooden raised bed for any openings in the structure that a slug could use to gain access to the bed by bypassing the fence - plug any openings with wooden shims or twigs
  • remove old wires and staples if you have an old electric fence that is no longer operational. One picture above shows last years wires (aluminum) and staples that I had to remove this year before installing the new galvanized wires.

Up to this year I have been using aluminum welding wire for my electric fence (MIG Electrode Wire).  This wire is great for bending around bumps or indentations on the raised bed but it is not very durable in the long run.  The wire corrodes easily especially where a slug or other unknowns have crossed or attempted to cross the fence.  A viewer of my other slug control video (http://youtu.be/EQ8RFlR0mD4 ) suggested that I try galvanized steel wire and that's what I went with this year.  I am writing this instructable well past  the growing season,  the galvanized wire has stood up quite well over the months since it was installed except for some small rust sections.

This spring I planted the garden and installed the new fence on the same day.  Obviously if you can't do it all in one day the fence must be installed and powered up first.

Step 3: Tools and Materials Needed to Make the Electric Fence

Tools and materials required
  • a staple gun
  • pliers to cut and crimp the wire (when connecting to the battery connector wires)
  • a blade screwdriver to remove old staples if present and also to screw the battery box to the raised bed
  • galvanized steel wire - any size from about 18 gage to 22 gage will do
  • 3/8 inch stainless steel staples
  • a box with a removable cover to hold the battery and keep the weather out
  • a 9-volt battery connector
  • a 9-volt battery
  • a multimeter would be handy to test the voltage but is not absolutely necessary (see slug testing in the video)

Step 4: Staple Wires to Raised Bed, Connect Battery, and Test With Meter or Slug

  • if desired you can use a pencil or pen to mark a line to guide you when stapling the wires in place
  • start stapling the galvanized wire to the raised bed near the location planned for the battery
  • staple every 8 inches or so along the wire
  • when the circuit around the bed is complete cut the wire allowing enough length to reach and connect to the battery
  • you can twist the ends of the wire together and direct them near the battery box location
  • start the second run at the same location but spaced about 3/4 inch form the first wire
  • twist and direct to the battery box as the first wire
  • create two holes in the battery box, ideally on the bottom,  for the wires to enter and connect to the battery connector
  • double check the wires around the raised bed and bend and staple any wires that are not flat against the wood
  • feed the fence wires into the battery box holes and twist them and then crimp them to the battery connector wires
  • install the battery and put the box cover on
  • use the multimeter to check the voltage between the two wires somewhere outside of the battery box (or use the slug test method - see video)
                                                           That's it - simple, inexpensive and effective!



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    156 Discussions

    A couple of notes on using 12-volts. First: I tried 12 volts (a series of AA cells) and found that the slugs were more often killed rather than just turned away. Second: NEVER use a high current 12-volt battery for this application (such as a car battery). The current supply capability is way too high and a short circuit between the wires would cause them to get very hot. However the 9-volt battery works just great as the internal resistance of the battery limits the current so there should not be a problem even with a short.

    I tried this with copper wire and a 9v battery, but it doesn't seem to be working for some reason; the snails just go straight past it. Does it have to be galvanised?

    7 replies

    Did you check if the copper wire was isolated? Most copper wires have a thin coating of isolation. You can either try to remove that or just get another wire.

    I stripped off the insulation, it was mains electrical wire. Didn't notice any slugs but there were snails that had got past.

    Hmm, what voltage did you use? 9 Volts is a minium I would say. If that doesn't work connect a big capacitor containing 400 V, that should make them fly off the fence.

    I used a rechargeable NiMh battery. I measured it at 8.4v.

    Maybe snails are less sensitive.

    Or maybe you keep the wires to far apart so that the snails never get the chance to get in contact with both of the wires at the same time.

    I dunno what you mean with velociraptors, I'm not from England neither can google translate define it ;)

    OMG!!! Bout fell outta' my chair!! A 'Velociraptor' was a type of dinosaur similar to a T-Rex but much smaller and faster and deadlier, as in ability to rip you apart ~ ~ ~

    Seems as though once they have been tingled by contacting both wires simultaneously they then associate just contacting a one wire as a bad thing. I refer to this in terms of "Pavlov's Slug" in the video :)

    I wonder if for a smaller area one could use those £1 solar garden lights.maybe not enough voltage. (about 1.5. i think) ?

    That looks good!

    For simplicity and safety I recommend a 9-volt battery for this application. The battery typically lasts for a full growing season (assuming the wires are mounted as shown in the instructable). In one experiment a number of years ago I found that 12-volts tends to "fry" the slugs rather than turn them away. Good luck with whatever method you might try.

    Look forward to your observations. Even though you have a reduced voltage (12 volts) and the mains connection is indoors it still might be a good idea to have the system connection through a ground fault interrupt type of circuit. There is always a chance of some kind of short between the primary and secondary of the transformer (if used).

    I've made this and it's fantastically effective, thank you. However I live in a wet area so my wire has rusted in places and the snails just crawl over the rust. What wire do you use? I considered using stainless steel but is this a good enough conductor?

    4 replies

    Yes I now use small diameter stainless steel welding wire. I forget the diameter but the small the better as it will be easier to form around the raised bed. In terms of electrical conduction it is just fine and it should last a good number of years. I have tried aluminum welding wire and galvanized wire but both have a limited life in this application.

    Great thank you, I shall look for some. My friends and family have been most impressed with your idea and think you could make a fortune if you sold this as a kit ?

    Thanks! Will pass on the kit idea but I would not have any objection at all to someone else giving it a try.