poisonous plants

Poisonous Plants: Do You Grow These?

Do you have poisonous plants in your garden?

I’d bet you do – and you may not be aware some of the common plants and shrubs we all love can be dangerously poisonous plants.

I started thinking about poisonous plants this week after reading a novel where a tincture of monkshood (Aconitum napellus) was used to poison a rival.

Turns out this tall perennial with pretty purple spikes of flowers is a favorite of many gardeners – a perfect background plant for borders. Now, knowing this, don’t rush out to pull up all your monkshood plants. The root contains the deadly poison – an alkaloid that can cause a whole host of symptoms and death. However, poisoning may also occur by picking the leaves without wearing gloves. The aconitine toxin can be absorbed through the skin, causing tingling, burning and numbness, and possible death if not treated.

Are there more poisonous plants may you be growing for their ornamental beauty that could be harmful – or even deadly? This list, from This Old House, describes twelve of the deadliest garden plants. Here’s the overview of plants you should never ever ingest:


Rhododendrons are one of my absolute favourite shrubs, and can be found in many gardens in the northwest.  It is completely toxic – the whole plant! Perhaps this is why deer will never touch it. Ingesting any part will cause vomiting, low blood pressure, a coma and death.

Lily of the Valley

This small plant with pretty white bells is a perfect groundcover plant for shady spots, and often the first flower of spring. But… the entire plant is deadly. Do not cut the flowers, as even the water you use in the vase will contain the toxin that can be fatal.


Another favourite flowering shrub – hydrangea – is one to be careful with. We love this one for the round clusters of flowers that last through summer and fall. The entire plant is deadly, especially the flower buds.


We all love the harbingers of spring – narcissus and daffodils – but did you know that the bulbs – and the entire plant – are poisonous and induce severe nausea, vomiting, convulsions and eventual death if consumed? That’s why squirrels, rabbits and voles will leave them alone, while they will cheerfully dig up and eat your tulip bulbs.

poisonous plants


I love the tall spikes of foxglove – beautiful spires of bell-shaped blossoms in purples and pinks that tower in the back of the ornamental border. The entire plant, especially the leaves, contain digitoxin, a powerful poison. Look, but don’t even think of consuming this one.


The larkspur – or delphinium – contains a high concentration of toxic alkaloids, especially the mature seeds. Grow larkspurs for the pretty blue flowers, but treat it carefully, and with gloves!


Oleander, with its fragrant flowers and dark green evergreen foliage, is a popular ornamental in warmer climates. The entire plant is deadly – especially its sap and leaves. A single leaf has enough poison to be lethal to a small child. Induce vomiting and administer charcoal immediately if any of the plant has been eaten.


Poinsettias, with their whorls of bright red leaves, are contemporaneous with Christmas. They are not likely to be planted outdoors unless you’re in a very warm climate, but are lovely as an indoor potted plant. The milky white sap is the dangerous part, so keep this plant away from cats, dogs and little children.

Purple Nightshade

Purple nightshade (Atropa belladonna) is occasionally grown for the bright black berries, but not often cultivated. Those berries are fatal, so its best not to include this in your garden. Incidentally, it’s a member of the nightshade family, which includes potatoes, tomatoes and eggplants.


Mountain laurel is a cousin to #1 on the list – common rhododendrons and azaleas. Like the rhodos, the whole plant is toxic when ingested. Mountain laurel has a number of different common names, including ivy bush, spoonwood, calico bush and American laurel. It is planted for its hardiness and its beautiful flower heads made up of many small pink blooms.


Mistletoe – that Christmas kissing vine – has pretty white berries that are particularly potent poisons for pets, so if you’re hanging up a sprig of this, make sure the berries stay attached. All parts of this parasitic plant are poisonous.

Water Hemlock

Water hemlock is one of the most poisonous plants in North America – striking you dead within 15 minutes if ingested in any form. If you do find it in your garden, it is likely a trespasser, especially if you have a meadow or stream nearby. It can be confused with yarrow, as it has similar umbrella like umbels of white flowers. However, it has a smooth stem and leaves, while yarrow’s leaves and stems are hairy. This is the plant that killed Socrates.

Other Common Poisonous Plants

There are many more poisonous plants than this small list. English yew is entirely poisonous, but of its red berries, only the seeds within are dangerous. Brugmansia, often called Devil’s trumpet is a newly popular ornamental with deadly alkaloids. Horse chestnuts are another, those popular spiky conkers. Seed, leaf, bark and flower are toxic  and should not be ingested. Others with poisonous parts include autumn crocus, bleeding hearts, castor bean plants, black-eyed susans, hyacinth, iris, lupins, morning glory, tansy, sweet peas, and squill.

Curious for more information on the twelve listed above? Go to the original article on This Old House website for more information on symptoms of ingesting these poisonous plants.

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