This is an odd question, perhaps; but first some background. I have an allotment garden (in UK) that I enjoy putting a fair bit of energy into, growing unusual vegetables and fruits. However, my enjoyment is marred by people regularly stealing my produce, so I'm thinking about how to discourage the thieves, and one idea I've had is to spray the plants with something harmless that leaves some sort of visible residue, and the put up a notice warning that the plants have been sprayed and possibly a recommendation that they contact the emergency department immediately if they feel sick, tired or have stomach symptoms.

But of course, there may be reasons why this is not a good idea; and if it is, which substance should I use - soap, chalk powder, ...? It should be something that is harmless and easily washed off, of course. What do people here think?

Alternatively I could put up wild-life cameras, well-camouflaged and with SIM-cards, so they live-stream pictures, but that feels a bit extreme (as well as expensive).

  • 4
    I was thinking that you could spray the produce with a product containing cayenne pepper (sometimes used to repel deer in the US), but you'd stand a pretty good chance of getting someone mad at you - possibly mad enough to destroy your plants. Your best bet is probably a six-foot tall fence, if your allotment allows that.
    – Jurp
    Mar 25 at 15:35
  • @Jurp and you have a low (but nonzero) chance of making someone be more likely to come back (if they like spicy food). Mar 25 at 23:55
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    Before you actually attempt this, you may want to check with Law SE -- I don't know about the UK, but there's often laws against "booby-trapping", and depending on how they're written they can encompass threats of booby-trapping (e.g. just having a "contact the emergency department" sign) as well, even if there's no actual risk.
    – R.M.
    Mar 26 at 14:31
  • 1
    You might want to put a sign that encourages donations. Depending where you live and who the thieves are this might work.
    – Buck Thorn
    Mar 26 at 20:48
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    If it's a common problem within the allotment then a collective response might be more effective. A chain link or weld mesh fence with a padlocked gate would probably deter most opportunistic thieves, after all, who is going to scale or cut a fence just to nick some marrows? Plus you talked about cameras as well. Individually this would be rather expensive, but divided among all the members it could be fairly affordable and will probably be more effective long term. Mar 27 at 23:13

3 Answers 3


I am sorry your garden is being raided, that is always frustrating.

I once washed colored chalk drawings off a sidewalk and I noticed some of the areas with lots of blue chalk looked a bit like Bordeaux mixture when it dried. I think your chalk powder, especially if you dye it a bit blue, would look like a pesticide.

Grape leaves with blueish white reside dried on the leaves

Alternatively, my own experience with two-legged garden raiders makes me want to imply something more viscerally unappetizing than 'pesticide'.


  • The Hu-manure Handbook has some classier images in the same vein.
    – MackM
    Mar 25 at 18:12
  • Like comments under the OP, this raises the legal question of whether humanure is allowed in the colony lot (or where at all). Even if it's fake it could bring unwanted attention.
    – Buck Thorn
    Mar 26 at 20:45

It's pretty common for actual pesticides to be mixed with a colored "spray pattern indicator". Without this there's little indication your expensive and dangerous chemicals have been used efficiently.spray pattern indicator blue colorant

You could spray some Homeopathic Pesticide (= pure water) mixed up with some indicator dye to show where it's been, etc.

But there are plenty of other "agricultural chemicals" that are totally harmless, cheap, certified organic, and could probably benefit you as well:

  • Neem oil is an insect repellent, antifungal, and more. Some people consider it actually good for you. It smells absolutely terrible
  • Foliar spray application is a good way to use organic fish fertilizer, which also smells terrible
  • Diatomaceous earth keeps bugs off, supplements soil calcium, and is a fine gritty powder that needs to be carefully washed off like fine sand
  • "Garden friendly fungicide" is just some GMO bacteria but idk that sounds scary?
  • etc.

If any treatments like this are performed, of course, it is good practice to clearly indicate it, i.e. "fungicide applied on 1/1/23" etc :)

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    Using stuff that smells terrible is perhaps less than ideal in a colony lot, and not just because others will mind, you will too.
    – Buck Thorn
    Mar 26 at 20:47

An approach with some research to back it is to put up images of eyes watching you. Especially if combined with words that direct the reader's attention to themselves and what they're doing, it triggers introspection and self-regulation, and reduces theft by quite surprising amounts. Casual thieves are frequently very sensitive to the feeling of being watched, and even if the eyes are obviously fake, it puts the idea in their heads. (Having dozens of creepy dolls heads staring at you might also be disconcerting.)

If you want to put up a sign warning of pesticides without either lying or getting into any possible legal trouble, I'd recommend looking up Gold, Ames and Profet paper on natural pesticides, which lists some of the nightmarish chemicals vegetables contain as part of their natural defences against the myriad things wanting to eat them. "Did you know that some of these plants contain allyl isothiocyanate, which causes genetic damage to mammalian chromosomes at a concentration of just 0.0005 parts per million? Be lucky." It's not a threat, it's just an interesting true fact, and if the reader misunderstands your educational efforts that's hardly your fault.

And the simplest material to spray on the leaves would be mud from the allotment itself. Entirely deniable, too.

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