The killers in your garden

Spring is the perfect time to get out and smell the roses. In every flowerbed, there’s some amazing chemistry going on – but we need to remember that some of our favourite plants contain deadly poisons. While they aren’t usually a danger for adults, they can be a risk for small children and pets.

Daffodils are some of the prettiest flowers that bloom in spring, but they’re also potentially dangerous. They contain large amounts of the poison lycorine, particularly in the bulbs. Lycorine is an alkaloid and surprisingly mysterious poison. We’re still not entirely sure how it works – nobody is willing to get poisoned to find out! Currently, the best guess is that it stops the body making more proteins. This poison is a great defence mechanism against animals trying to eat the plant. It also helps it to compete against rival plants, as the bulbs can kill roses and cabbages nearby. If you want to see how poisonous daffodils can be in a vase of other flowers, add some daffodils and watch how most plants die much more quickly than those with no daffodils present. This is because of another poisonous alkaloid, narciclasine, and sugars and polysaccharides in the daffodils’ mucilage increasing bacterial growth in vase water.

Perhaps the most famous killer that takes root is Atropa belladonna, or deadly nightshade. Nightshade’s danger comes from its high content of tropane alkaloids – a tropane is a chemical ring with nitrogen in the centre, like the hub and spokes of a bicycle. This includes the toxin that gives the flower its name, atropine, which disrupts the central nervous system’s ability to control the heart rate, with potentially deadly results. It was used as a beauty aid in the past although it is poisonous, and today, we use small doses of atropine to treat glaucoma. And not all members of the nightshade family are dangerous: it also includes tomatoes, potatoes and aubergines. But pets often can’t eat the same things we do: onions and raw potatoes can be dangerous for cats and dogs.

One of the most well-known dangers lingering in our herbaceous borders, and in the wild, are foxgloves. These pretty, purple plants produce cardiac glycosides – steroids attached to a sugar group – which affect our hearts. But they are far from the only pretty plant to pose a risk. Lilies are a lovely addition to gardens and flower vases, but they can be deadly for cats. This is because some lily species contain calcium oxalate crystals, which don’t dissolve in water. In humans, these can result in mouth and throat irritation and kidney stones, which can be very painful. In cats, lily poisoning can be fatal.

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Atropa belladonna, or deadly nightshade, gets its name from the toxin atropine

Source: © Jon Benedictus/Shutterstock

A plant for your lover – foxgloves produce cardiac glycosides, which affect our hearts

Source: © Nicholas Taffs/Shutterstock

Lillies' insoluble calcium oxalate crystals can be fatal for feline friends

Source: © Cuppyuppycake/Getty Images

Giant hogweed’s sap contains furocoumarins, a phototoxin

Source: © Ernie Janes/Alamy Stock Photo

Sun, sap and blistered skin ... take care near giant hogweed

Source: © Grisdee/Shutterstock

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And it’s not just the plants we want that pose a hazard; some weeds can cause serious harm. Giant hogweed is one of the most easily recognisable plants in the UK, with a tall, thick stalk that erupts into bouquets of small, circular white flowers. Related to carrots, it’s an invasive species from south-eastern Europe – and one any gardener needs to handle with care. Giant hogweed’s sap contains furocoumarins, which can enter the nucleus of skin cells. Furocoumarins are phototoxic and when exposed to certain wavelengths of ultraviolet light (such as sunlight), react with our DNA, causing inflammation and the cells to die. This means that if you get giant hogweed sap on your skin and stay in the sunshine, your skin will soon turn red and begin to erupt in painful blisters. The same can happen to cats and dogs, although their fur gives them some protection.

All these plants can be nasty, but fortunately you can avoid these risks. Don’t eat plants you don’t know are safe, don’t mix your daffodil bulbs with onions and if you’re going to get rid of giant hogweed, make sure you wear gloves and, ideally, a pair of glasses too. Finally, to look after any animal friends, check to see which plants are poisonous to that species, watch for signs such as vomiting and diarrhoea and keep an eye out when pets are in the garden or on walks.