Protect Your Tomatoes With A 9V Battery

Growing fresh vegetables at home is a popular pastime, even moreso in a year when we’ve all been locked inside. However pests can easily spoil a harvest, potentially putting a lot of hard work down the drain. [Matt] of [DIY Perks] isn’t one to give up his tomatoes without a fight, however, and came up with a solution to protect his plants.

The trick is to take advantage of the mildly conductive slime excreted by snails as they travel along the ground. To protect potted plants, [Matt] places two strips of copper tape around the perimeter of the pot, spaced about a centimeter apart. Each strip is connected to one terminal of a 9 V battery. When a snail attempts to cross the strips, it completes a circuit between the two, and the electrical current that flows irritates the snail, forcing it to retreat.

[Matt] notes that no snails were harmed in the making of the video, and that the solution is far kinder to the slimy critters than poisons or traps. He also goes so far as to demonstrate alternative solutions for garden beds, as well. We’ve more commonly seen [Matt] working with lighting, though it’s great to see he has a bit of a green thumb, too. Video after the break.

56 thoughts on “Protect Your Tomatoes With A 9V Battery

      1. I’d put a constant current limiter in series then.

        In case of excessive rain shorts the copper.
        LM317 and appropriately sized power resistor, though cheap and simple, it’ll probably require heatsinking the LM317, but this way there’ll be no fuse to worry about.

          1. Highish value of resistor followed by a capacitor. When they touch, the capacitor discharges to give them a brief shock, and then slowly charges again through the resistor.

        1. Stainless steel wire and a resistor to limit the current, to both limit any corrosion/etching and prevent accidental shorts from water. As DainBramage says, the snails probably don’t need a lot of current.

        2. Is the LM317 a good current limiter? Over what voltage and current ranges? Is there a voltage drop of any sort? I tried some recently and had no end of trouble with them. Are they better than just using a power limiting resistor on its own?

  1. I use alternating overlapping aluminium and copper foil tape instead. Each slug/snail is it’s own electrolyte.

    I don’t use 9V batteries as a fresh one, in my experience, means dead snails which have fallen off my rasied bed.

    All this said so long as youre careful snails are good eating.

      1. For starters, cook the little morsels. Technically, wild snails & slugs are edible, but you don’t know what they’ve been eating. This often includes poisonous (to us) mushrooms, etc. If you enjoy eating them then the safe approach is to farm them such that their environment & food is controlled.

        1. You harvest them and keep them for a while on a bed of oatmeal.
          They will secrete nasty stuff and eat the oatmeal.
          Same thing if you want to eat Caribbean land crabs, these buggers even eat manchineel leaves, a tree so toxic you can’t even shelter under it when it rains.

      2. For starters (and most importantly) as RustyHydrogen, cook them, thoroughly. The cases of rat worms or other parsites are from raw snails typically eaten on a dare but of course you could always get something from undercooked food – it doesnt have to be totally raw.

        And I’m a fraid yes – this is ‘riskier’ than supermarket shelf food. Even if you take all precautions cooking garden snells is a risk. But it’s very safe actually, very environmentally friedly and better than just stamping on them and leaving them in your garden!

        It’s also a very long process, but a labour of love.

        The general process is to ensure that the snails are healthy – to do this you monitor them for about a week total, control their diet and keep washing them. This means you get to control what’s in their gut – it’s not poisonous enough to make the snails drop dead, and they are healthy enough to have not ropped dead!

        After a heavy downpour pick up medium sized snails that appear well – shell intact not bubbling etc.

        Collect them in a large bucket one they wont escape from I used an old plastic 5 gallon primary fermentation bucket. It’s just food safe with a small hole for air and a lid that clicks down.

        Each day wash out the bucket rinsing snails – inspecting them – and adding in food for them a carrot is ideal as it dyes their poop orange.

        Keep doing this while you collect enough snails I go for 4-8 per person. Depending on the size of the meal.

        Once you have collected enough and every snail has been monitored for at least 3 days – and they are pooping orange (so their gut is cleanish from contaminated foods). They haven’t died of poisoning or illness. Fast them for about 3 days.

        This means they aren’t full of poop.

        Rinse them thoroughly. Put them in a bowl in the fridge to render them insensible.

        (Brief note some chefs will salt the snails to encourage the slime and rinse it off. Idk if this makes a diferent and I don’t bother).

        Now… cook them. This is typically a short boil 3 minutes minimum (wish I had a good source for this https://www.nationalgeographic.com/news/2018/03/dont-eat-slugs-snails-rat-lungworm-brain-parasite-health-science/).

        Remove the snails, cut off the hard ?foot or whatever it is.

        Now you’ve got snails to make a dish! You’re not done yet Im afraid.

        Then you can make escargot (basically dip in garlic butter and bake in the shell – scrub the shell!).

        But I prefer to shallow fry in garlic butter, cover in bread crums and serve without the shell.

  2. I’d just like to say that copper tape is awesome. I was lucky to expense a fairly hefty 3M roll to work many years ago and later used it to bridge corroded keyboard traces on an Atari 800xl that had been stored in garages for 30+ years. Have also used it in various RF projects.

  3. I find a single copper strip works fine, no battery. An electrochemical effect puts them off. But snails may vary? Encourage birds like thrushes to keep numbers down.

    Small slugs will also climb up the bottom of a container via the drainage holes.

    I’m slightly concerned about his pond for a 9v he built from the green jar lid… I think that design might need some work before it rains.

      1. Because it’s set on a nonconductive surface; looks like a stone countertop. But Alex Rossie above nailed it: put two different metals and the mucus will complete the battery; like chewing foil when you have amalgam fillings.

  4. of course, you do realize that you just shortened the human races dominance of the earth by a few thousand years. you are forcing the evolution of those snails and will cause them to be smarter. then we are all doomed!

  5. Slugs don’t eat tomatoes; but I have dozens of other plants to protect so the battery idea is not going to be practical. I use the non-toxic (to other critters) slug bait around them, clean up the plant litter, use beer traps, and squish them at sundown. Hundreds a night sometimes. I have hiding places for snakes and toads, and perches for birds.

  6. Obviously you dont know anything about electricity? You realize you have to touch both end of the + and – poles to get a shock. It can even go from + to – in stead of how it is here – to + same thing, it needs to have both end touching to conduct a shock.

  7. And SLUGS… Got snails on the brain but SLUGS do as well…all Slugs are are snails without shells, they eat the same things snails do if not more cause they dont have to manever with a shell on their back.

  8. 7,000 VAC also works against slugs. At 30 kHz, seems to keep cats away too.

    An old colleague working for Boeing used something similar to discourage a bear from steeling his chicken food. Used something like 10 mA at 50 kV though.

  9. Excellent Write-up, I especially liked the stand-alone version that never occurred to me. I tried to use the Copper wire + Zinc-strip solution many years ago as a “passive” electric fence by using the slug/snail as the electrolyte, but found the battery-powered solution with some free and corrosive resistant recycled stainless steel wires far more effective (thought epoxy dots to affix the wire was tedious. Now that we have adhesive copper tape this is a great and simple answer any kid could do. Also, remember all those 9V batteries you throw out each time your smoke alarm BEEPS? Use those on This project., they have plenty of power left for this after their short 6 months on the ceiling. Winner-Winner Tomato/Lettuce dinner for every season of home fire safety!

      1. A piece of hairy blanket of about 30×30 cm around the stem has perfectly done the job for me. Imagine a snail trying to crawl on a blanket and you will get the idea. For the snail this surface is like a man walking on spikes. Will not do it just for food. The snail quits and searches elsewhere for food. Works even when blanket gets wet but not as good.

    1. You can get a heavy duty flyscreen meant to be clawproof. At least one could find it in Ontario, Canada 5 years ago. However it is not as fine a mesh, so if midges and no-see-ums are a problem locally, then one might have to dual layer it with a normal screen, putting the regular stuff the opposite side to the problem. However, if you’re going to end up double layering anyway… I have also seen 1/8 or ~3mm mesh “hardware cloth” wire netting, which should protect a screen mesh the other side of it pretty well. Either of these solutions might take some special fettling of the screen frames, either heaps of brute force to jam the spline/roving into the channel with double layers of mesh, one of which is thicker, or routing out a slightly wider channel to compensate.

      However, my experience with a cat was that although he inflicted some damage on the screen, his major method of escape, the crafty bugger, was pulling at a corner repeatedly until the screen was pulled out from the spline, then he’d pull at the spline until enough of the corner was flapping loose to climb out. He was quite mechanically minded that one, he’d figured out doorknobs but most of them were two stiff for 2 paws to get enough grip to turn. I saw that rascal flip the catches on a suitcase once too.

      Although generally for screens, the fibreglass and aluminum variety, I find them to get brittle with age. The fibreglass types seem to suffer from sun damage, and the aluminum ones from oxidation. About 3 years seems to be the period they retain “as new” strength, declining after that to around 10+ years when they may as well be newspaper.

  10. No one has mentioned salt. I use something better, sprayed on non sudsing liquid household ammonia. I’ve seen slugs slime their way out of a heavy dose of salt which isn’t good for the plants and soil anyway. The ammonia turns into nitrogen and is good for the soil. It’s fun to zap them with one shot of a trigger squirt bottle and watch ’em writhe.

    Perhaps slow motion video analytics and an AI robot gun setup could go after them in controlled areas like greenhouses.

    The only time speed up video is fun to watch, snails on foraging mode. See collisions happen, not in real time. The reverse of fireworks every time their antennae get a hit of voltage.

    Look at that S car go!

    1. As I mentioned above (or below) I used Stainless Steel wires recycled and separated from a used bicycle brake cable for the electrodes (that, after trying a year of Copper/Zinc failures of self-decomposition in in a ‘passive’ setup). As I had to fix these steel wires to the surface of the plant containers or raised bed walls, I used epoxy. The advantage was not only did the ‘powered’ conductors not decay, but current loss was diminished during wet weather due to the wall / surface separation. The battery joints were crimped (or twisted on if you have no crimping mech) then epoxy coated to seal out moisture. It is tedious to apply epoxy ‘posts’ for the ‘fence wires’, But the copper used in this blog is so quick, cheap, FLEXIBLE and replaceable each season if needed.. (always disinfect your plant pots each season). Also a used 1.5v AA or AAA battery also gives a good deterrent Zap. (Your TV remote battery-milage may vary upon your local lock-down rules This Year.)

      1. (since I joined the Joule Thief Cult, I solely use old 1.5V cells for LED garden projects, and ‘used’ 9V alarm batteries for the pest control). Watch me salivate standing in front of the local battery recycling drop point….

    2. I did this a few years ago, with aluminum duct tape strips and expired 9V batteries that had kinda 7V on them. It worked for a year or so. But battery clips corroded and/or aluminum oxidized.

      Early on, I did watch some of the slugs testing out the barrier, and they really don’t like touching the second strip, but it doesn’t seem to do them any harm either. But because they smelled the basil growing above, they really wanted to get up there, and kept testing it. Any hole in the defenses will be found.

      I now grow basil up on the balcony where the slugs simply don’t go. It’s less upkeep. But the tape/battery thing absolutely did work for a time.

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