You have probably heard the gardening tip about lining your pots or beds with pennies, which supposedly act as a slug barrier, because they "get an electric shock."If you know anything about electricity, spend any amount of time thinking about this, testing it or just looking up credible sources you'll realize that this is complete nonsense, it is one of those urban myths which refuses to die. Sure it looks pretty, but it's definitely not worth wasting your time or hard-earned pennies on, especially if you really want to protect your lettuce. But it DID get me thinking; what if I added a power source to actually deliver an electric shock to a slug trying to intrude upon my lettuce... would it work?
It turns out I am far from the first person to have thought of this, and you'll find plenty of videos showing one version or another. I decided to try my own, solar version, using the electronics from a broken solar garden lights, and some copper tape I had in my stained glass toolbox.
Disclaimer: in spite of the slightly sensationalist title, this won't actually kill slugs or snails, assuming you limit yourself to the voltage of a common battery (and I would not recommend using higher voltage unless you hate your pets and your kids -- and yourself!). But it will deliver enough of a shock to make their tiny and sluggish brain understand that your juicy plants just aren't worth it, and they'd be better off going next door.
I promise to update this instructable when the result of my double bed studies come in (since this raised bed is in a community garden, I will have plenty of non-electrified beds for comparing results). If I am lucky enough to win one of those stop motion cameras in the garden contest, I'll include the video surveillance footage as well.
Step 1: The Circuit
The idea here is that you are creating an open circuit, and the slug (or snail) trying to cross over the barrier touches both lines at the same time, which closes the circuit and allows the electricity to flow, delivering an unpleasant shock to the unsuspecting mollusk. After a few attempts, it should dawn on his sluggish brain that he'd be better off looking elsewhere for his dinner.
In reality, since you are creating an enclosure around your raised bed you will create 2 parallel loops rather than the straight lines drawn her on the sketch, but basically this is the circuit. You will connect one loop to the + and the other to the - side of your battery (it doesn't matter at all which) and you're golden!
Step 2: Materials
Basically, all you need is wire and a waterproof low voltage power supply.
For my power supply, I found an old garden light which was thrown out because the stake had broken -- but the light worked just fine, so the electronics were intact, and ready to go in a water-tight enclosure. These are so cheap now you can easily buy one for the purpose of ripping it apart -- or you can simply get a battery, put it in some sort of weather-proof container, and skip the whole solar thing.
For the wire surrounding your bed, you can use anything which will conduct electricity: copper, galvanized steel, or if you're simply itching to waste money, solid gold is great too. I happened to have some copper tape left-over from an old stained glass project, but otherwise I think galvanized steel wire would be the easiest and cheapest solution. You'll need a staple gun to attach the galvanized wire to your raised bed, but that's not necessary if you use the copper tape.
In addition to this, I used some regular (insulated) electric wire (which I cut off some old obsolete piece of electric equipment someone was throwing out), so I could place my solar panel wherever I wanted. Then I used solder and a small soldering iron to connect the wire to the battery pack and the 2 loops surrounding the raised bed, and finally some heat shrink tubing to insulate and cover my soldered connections.
Step 3: Solar Panel Preparation
If you're buying a solar light, choose one (like the ones used here) with the battery pack and polar panel separate from the light. This will just make your life easier, because all you'll need to do it cut off the light, and connect the wires to your extension cord. You will also need to cover the light sensor, otherwise your circuit will only work at night (your garden light is designed to turn on when it is dark, so you've got to cover the light sensor for it to work during the day). I covered the sensor with three layers of black electric tape which was more than enough.
Connect the solar battery pack to an extension cord, so you can place it wherever you'd like.
You can buy wire, but it's just as easy and cheaper to cut it off any piece of discarded electronics. You only need a very small wire for this low voltage, but it doesn't hurt in any way to use a regular, thick wire, so use whatever you have handy.
Before you solder the wire to your battery pack, slip some heat string tubing over each wire so you can cover and seal the soldered connections when you're done. I put two small pieces over each individual wire, than a bigger one to cover the whole connection, for extra protection since this will live outside.
Step 4: Prepare the Bed
You want to create two parallel, uninterrupted loops around your bed using exposed wire of conductive material, so that the mollusk much touch both wires at once (thereby connecting them with its slimy wet body) when it attempts to cross the line.
I had copper tape, so that's what I used, but it is important that you use a single, long piece to create each loop. If for some reason you cut the tape, you should add a bead of solder over the joint to make sure your circuit is not broken; since the adhesive on the tape is not usually conductive, overlapping two pieces will not necessarily work, even if it looks like they're touching.
To make the tape turn by 90°, fold the tape at a 45° angle away from the direction you're planning on going to, then fold the tape back over itself towards your chosen direction. That way you can turn without cutting the circuit.
Step 5: Final Assembly
Place your solar panel in a nearby sunny spot (keeping in mind that plants will be growing, and possibly adding shade), then solder the wires from the battery pack extension, one to each loop (it really doesn't matter which). As long as these wires can't touch each other, there's no need to insulate the connection: the whole point of this circuit is to have exposed wires to electrocute your slimy enemies.
When I'm not gardening I'm usually making pop-up cards. Check them out!