Perhaps the most talked-about bit of an already very talked-about garden is Alnwick Garden’s Poison Garden. You’re only allowed inside the locked gates with a guide, no doubt mainly because of those pesky health and safety types but in fact a handy way of emphasising just how dangerous these plants can be.

Here you’ll find plants in cages. A cannabis plant grown with a special Defra license and a (admittedly a little weedy-looking and therefore not very scary) Datura or two are among the prison population.

There are also a lot of very familiar plants, and as someone who likes to think they know their plants well enough to be pretty sure which ones to avoid, it was distinctly unsettling to learn that ivy, box, and laurel are among the harmful plants with a place in this garden.

So – if you spot any of this motley crew lurking in your beds and borders, or indeed in the hedgerows and fields: be afraid… be very afraid…

Hemlock is a member of the parsley family and looks alarmingly similar to cow parsley in the wild – but it smells like mice and has bright pink stems

Hemlock (Conium maculatum): Probably the most famous poisonous plant of them all, and still found commonly in the countryside. When Socrates used it to commit suicide I don’t suppose anyone mentioned to him that it paralyses you from the feet upwards. So you’re entirely conscious while it numbs first your legs, then your torso, and finally stops your lungs from working so you suffocate. Meanwhile the brain is entirely unaffected, and remains lucid throughout. Mmm. Nice.

Ivy (Hedera spp): Ever noticed when you’re pruning a big mass of ivy that you start coughing? That’s not just because it’s dusty under there because it’s the first time you’ve clipped it back for centuries. You’re breathing in saponins, which in quantity can lead to laboured breathing, convulsions and eventually coma. So next time, wear a face mask.

Box (Buxus sempervirens): If you’re clipping box hedges, don’t wander off and have a cup of tea before you pick up all the little bits that have dropped on the ground. As they dry, they release buxine, and if you touch it, it’ll give you an irritating skin rash.

Even boring old laurel can bite

Daffodils (Narcissus spp): People eat daffodils thinking they’re onions. No, really – it’s true. Unfortunately the law of natural selection doesn’t apply here: though eating as little as half a bulb gives a nasty stomach complaint, it won’t rid the world of someone with a criminal lack of common sense.

Laurel (Prunus laurocerasus): Now this one came as a complete surprise. If you stack all your prunings in a big bag and stuff them in the back of the car, then think, “oh sod it, I can’t be bothered to go to the tip today” you will pay for your laziness with a car full of cyanide fumes in the morning. Apparently entomologists kill bugs by putting them in a jar with crushed laurel leaves. Much the same principle, really.

Autumn crocus (Colchicum autumnale): Crikey, you don’t want to be mistaking this one for onions. In fact most people don’t: they mistake it for wild garlic, which it greatly resembles (a lot more than daffodils resemble onions, I suspect). Symptoms sound like something out of a particularly gruesome episode of Casualty: convulsions, cardiovascular collapse and multiple organ failure. Apparently it’s a lot like dying of cholera.

Rue is deadly – though the bees don’t seem to mind

Rue (Ruta graveolens): Ever heard of the phrase, “Rue the day”? As in, “I rue the day I ever planted this damn thing in my herb garden?” Well though this is a very pretty plant, and found in lots of people’s herb gardens, it’s really quite a vicious little thing. Brushing against it, especially on a sunny day, can blister skin to the point of burns: what’s really extraordinary though is that rue is often recommended (and grown in people’s herb gardens) for rubbing onto the skin as a mosquito repellent. Please don’t do this: mosquito bites will seem as the kiss of angels in comparison. Eating it causes acute gastroenteritis and eventually liver failure, though fortunately it tastes disgusting.

I’ve left out the obvious poisonous plants we all (hopefully) know about: the monkshoods, cuckoo pints and nettles which all gardeners should handle with care. But there are a whole lot more – aquilegias, cimicifuga, periwinkles, snowdrops and daphnes to name but a few – which I could have included and which you should know about.

I’m indebted to John Robertson, a former guide at Alnwick’s Poison Garden, for supplementing my patchy recollections with extra information: and if you want to know about the bits I’ve left out, I can only direct you to his exceptionally good website where all these plants and more are described in gruesome detail.