Garden visits Gardening Poisonous Plants

The Toxic Plants Garden: A Halloween Discovery

A toxic tree, poison sumac (Toxicodendron vernix), rises above the Toxic Plants Garden in its striking Halloween colors. Photo: Jardin botanique de Montréal (Robert Mineau)

Here’s a bit of a Halloween theme: a garden of poisonous plants, a place where you might expect to find ghouls and goblins and miscreants of all sorts. There’s one at the Montreal Botanical Gardens, one of the world’s largest botanical gardens, with over 21,000 species. 

Map of Monreal Botanical Garden showing the location of the Toxic Plants Garden
The Toxic Plants Garden is just a very tiny corner of a huge garden. Ill.: Jardin botanique de Montréal

The Toxic Plants Garden, started in 1940 under the guidance of the Garden’s first curator, Henry Teuscher, is fairly well hidden, in a little rectangular section with walls and a fence right next to the Medicinal Plants Garden … a logical choice, since so many poisonous plants are used for medicinal purposes (think of foxglove [Digitalis purpurea], source of the heart medication digitalis and the opium poppy [Papaver somniferum] from which morphine is derived). There are signs warning you the plants are poisonous.

The objective of the Toxic Plants Garden is above all to present visitors with a sample of native, naturalized or cultivated species that visitors are likely to encounter in a garden or in a natural environment. Some of these species can cause poisoning following accidental ingestion of part of the plant or eating the fruits. Others can cause skin reactions or respiratory allergies. So, don’t touch them or even breathe in their pollen! Scary!

There are some 40 poisonous plants in the Garden, including poison ivy (Toxicodendron radicans), water hemlock (Cicuta maculata) and poison sumac (Toxicodendron vernix).

Castor bean plant
Ricin or castor bean (Ricinus communis) is a popular garden annual and a medicinal plant (remember castor oil), but also contains a deadly poison. Photo: Jardin botanique de Montréal (Michel Tremblay)

Some are of historical interest. Who doesn’t know that Socrates was killed by ingesting a decoction of poison hemlock (Conium maculatum) in 399 BCE, for example? Others made waves more recently: only a few weeks ago (September 2020), there was a ricin scare when a mentally unstable Quebec woman mailed a ricin powder tainted letter to the White House in an attempt assassinate the American President Donald Trump.

Not Such a Frightening Visit

Poison ivy with orange leaves
Fall colors of poison ivy (Toxicodendron radicans). Photo: Jardin botanique de Montréal (Pascale Maynard)

I’ve visited this garden many times and don’t find it at all lugubrious. Instead, it’s a charming little corner with some fascinating plants that you never see elsewhere. I mean, most botanical gardens would never think of growing poison ivy, yet it’s a highly attractive plant, with beautiful shiny leaves that change to spectacular fall colors.

If you’re an amateur botanist who wants to learn to identify some unusual plants, it’s also a great spot to do so. Where else will you find such a wide range of deadly, almost never grown plants in one place?

Poison hemlock with umbels of white flowers.
Poison hemlock: it looks just like a host of other umbellifers. They’re certainly not plants to experiment with! Photo:

I enjoy looking at the venomous vegetation and trying to learn to recognize the individual plants, although I must admit that, to me, poison hemlock looks just like the sweet cecily (Myrrhis odorata) that I munch on all the time in my own garden. (Reminder to myself: if you find what looks like sweet Cecily in the wild, it’s best not to do a taste test.)

Giant hogweed seed cases.
Giant hogweed (Heracleum mantegazzianum). Note that is is a hogweed, not a hugweed: touching it can lead to severe skin irritation. Photo: Daniel Gélinas (Jardin botanique de Montréal).

It’s likewise a great place to take children. They find poisonous plants fascinating and will want to know all about just how the plants can kill. Supply as many gruesome details as you can: they’ll lap it up! I further recommend pretending to bite into an imaginary leaf, then clutching your throat, choking and falling to the ground as spasms take over your limbs and your eyes finally close in simulated death. They’ll love that! Of course, even as the visit titillates the morbid side of their nature, it teaches them not to put just any plant part in their mouth. And that’s a good thing!

Other Toxic Plants Gardens

The Toxic Garden at the Montreal Botanical Garden is not alone. There are others. Here are a few I know about:

The gate to the Poison Plant Garden at Alnwick Garden is certainly ghoulish enough! Photo:

The Poison Garden at England’s Alnwick Garden seems to get a lot more press than Montreal’s one and openly promotes its deadly denizens. It’s been called “the world’s most dangerous garden”: now, that ought to attract crowds! It’s a more recent garden, dating only to 1996, yet contains some 100 poisonous plants. I haven’t seen it, but I’d love to visit.

The Poison Garden at Blarney Castle. Photo:

There is also a Poison Garden at Blarney Castle in Ireland, said to contain wolfsbane, mandrake, ricin, opium and cannabis, among other toxic plants. A warning sign says children must be accompanied by adults: a wise decision. It opened in 2010, the year after I lasted visited Blarney Castle, so I haven’t see this one either. (And no, I didn’t kiss the Blarney Stone!) 

The Orto Botanico di Padova is small (maybe condensed is a better word), but fascinating and well worth a visit. Photo:

The Orto Botanico di Padova (Padua Botanical Garden) in northwestern Italy, not far from Venice, which I have visited, dates back to 1545 and is best known for being the world’s oldest botanical garden that is still in its original location. It’s a UNESCO World Heritage Site and fascinating to visit, with its 16th-century buildings and dense, circular, systematic planting. It’s mostly dedicated to medicinal plants (the original purpose of botanical gardens was to bring together medicinal plants from all over the world) and plants are placed according to which of the four “humours” they were felt to belong, an old concept based on ancient Greek medicinal theory. The poisonous plants garden is off to one side. 

There may be other poisonous plant gardens. If so, let me know and I’ll share that information.

? Happy Halloween … but do skip those hemlock bonbons! 

Garden writer and blogger, author of 65 gardening books, lecturer and communicator, the Laidback Gardener, Larry Hodgson, passed away in October 2022. Known for his great generosity, his thoroughness and his sense of humor, he reached several generations of amateur and professional gardeners over his 40-year career. Thanks to his son, Mathieu Hodgson, and a team of contributors, will continue its mission of demystifying gardening and making it more accessible to all.

2 comments on “The Toxic Plants Garden: A Halloween Discovery

  1. One of the all time LAMEST projects that I was ever involved in was the so-called ‘restoration’ of a tiny section of the Guadalupe River through San Jose. The developer who had built condominiums there had to agree to the restoration of that section of the River to get permits for development. The ‘restoration’ landscape involved a bed of poison oak, just because poison oak might have potentially been native to the site long before anyone can remember. There were many more natives that did not make the cut. My initial concern was that there was no source for poison oak plants. Well, what is crazier than the landscape was that there is a nursery that grows poison oak!

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