I recently had a rather intense conversation with a friend regarding a particular plant that I grow each year as part of the tropical garden. Following a documentary I’d seen that featured the assassination of an investigative journalist in 1973 in some rather bizarre circumstances, I asked my friend, who is a doctor, how it was possible to kill someone who hasn’t actually ingested the plant and how much of the substance was needed to do it. Now, I thought I was asking a fairly benign question, but was somewhat taken aback by his response. Admittedly text is probably not the best way to have these sorts of discussions, but the questions have been burning away since I watched the piece. As an aside, I remember years ago a conversation with another friend who is an airport security instructor, and over coffee one day, we sat and discussed the various elements he’d had to research and teach, this included a bomb-making manual that you can find online – apparently, although if you do download it you can expect a knock on your door from the anti-terror squad, he said. With this in the back of my mind, I thought it perhaps better to ask someone in the know the ins and outs of killing someone with this plant rather that risking googling it, if you get my thinking!
His reaction shocked me for several reasons. Not least because it’s a very commonly used plant in the UK where it’s a fast growing tender annual. I’ve watched Carol Klein sow the seeds in her series ‘Life in a Cottage Garden’, in fact it’s often used in a variety of planting schemes that are open to the public and the seeds are easily purchased from seed suppliers, although they do have ‘poisonous’ in big red letters on the packet. It’s fairly rapid to germinate, sizes up quickly and if the weather conditions permit, it should give a great display of fabulously architectural palmate leaves, a must in a tropical theme and as they are not hardy at all, at the end of the year they are composted and then the whole process begins the following year.
So, what is this plant? Well, its Ricinus communis – the castor oil plant. There are a few varieties from the smaller ‘Impala’ with its purple leaves to the exotically named ‘Zanzibarensis’ that, if you are lucky, can get to 8 foot tall with 2-foot-wide leaves. It has a similar look to the ultimate Jurassic jungle plant the Tetrapanax papyrifer.
While my friend was adamant that I shouldn’t even handle the seeds and was genuinely shocked that I even had seeds in my possession it got me thinking about how many common plants that we gardeners grow are actually toxic, and let me tell you, the list is a long one.
In Northumberland, Alnwick Garden has its very own Poison Garden, complete with gates depicting skull and crossbones and the ominous warning that these plants can kill. According to their website you can visit the “small but deadly Poison Garden—filled exclusively with around 100 toxic, intoxicating, and narcotic plants. The boundaries of the Poison Garden are kept behind black iron gates, only open on guided tours. Visitors are strictly prohibited from smelling, touching, or tasting any plants, although some people still occasionally faint from inhaling toxic fumes while walking in the garden”
The Duchess of Northumberland began the garden in 2005 in the vein of the medieval medicine gardens, but she is quoted as saying "The line between kill and cure is what I'm interested in. The story of how plants can cure, I find pretty boring, really. Much better to know how a plant kills." Sounds like a woman after my own heart!
It might come as a bit of a surprise to find out which common plants are actually toxic. Not all are as deadly as Ricinus, but some are. Take Aconitum napellus, that’s Monkshood to you and me. This tall, stately flower is considered the most poisonous of the UK’s native plants and according to the Royal Horticultural Society “All parts are highly toxic if eaten, all parts may be harmful through skin contact” and gloves and protective equipment should be worn when handling.
The beautiful little bells of the fragrant Lily of the Valley, convallaria majalis, bely its deadly intentions. It contains around 38 different cardiac glycosides (cardenolides) – which are highly toxic if consumed by humans or animals.
No cottage planting scheme would be complete without the statuesque, prolific self-seeder, the common Foxglove, Digitalis purpurea. Foxglove contains chemicals from which the prescription medication digoxin (Lanoxin) is made. You would think that the humble foxglove might be one of the good guys but no. For some people just touching the plant can lead to severe irritation and even anaphylaxis. Ingestion of any part of the plant is going to make you pretty sick and can even cause irregular heart function and death. I know what you are thinking, why would anyone be daft enough to eat it? Well not all plant poisonings are intentional, apparently most poisonings with this plant take place when it is mistaken for comfrey, the moral of course to be 100% sure of your plant identification before eating it.
What about some of the less obvious, toxic plants? We are just a couple of weeks away from Spring and already the daffodils are making an appearance. But guess what these are toxic too! In sensitive people, even smelling them can be enough to induce vomiting. There are about 20 different toxic alkaloids that have been identified in daffodils, the most common being lycorine, a toxic crystalline alkaloid which ironically seems to also have therapeutic benefits - Lycorine is active in a very low concentration and with high specificity against a number of cancers both in vivo and in vitro and against various drug-resistant cancer cells, but that one is best left to the experts. If you are interested in reading the study though here’s the link - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7127747/
Our other favourite spring flower, the Tulip, well that’s also toxic. Back in WWII in Holland, the bulbs were eaten as an onion substitute but all parts of the plant except the petals, however, contain toxic compounds that can cause illness.
For many plants, producing toxic compounds is part of the survival strategy. Quite simply, its stops them being eaten by a variety of predators. Some plants even defend their territory by secreting toxic substances into the soil, preventing any other plant from spreading into their location. You can read more about this here - https://www.mpg.de/9731123/plants-allelochemicals-competition
As gardeners we need to understand our plants. The often touted ‘right plant, right place’ as well as knowing growth habits and seasons of interest are important, knowing which plants can harm or kill us is essential.
What dangerous plants are lurking in your garden?
For a list of potentially harmful plants see the RHS website -