Do You Have Poisonous Plants in Your Garden?

  • Post published:03/23/2018
  • Post comments:2 Comments
Castor bean plant
Castor bean plant – one of the first poisonous plants I knew I had in my garden

Few of us hear much about castor oil anymore, but my childhood memory is that it was a common laxative and I never imagined there was a castor bean plant and it was one of the very poisonous plants  Even as an adult I never gave a thought as to where castor oil came from so it was with great shock that when I admired a beautiful big plant with dark red-tinged leaves and prickly red seed cases it was identified as the poisonous castor bean (Ricinus communis) plant.

I continue to admire castor bean plants, but I would be too nervous to grow it in my garden. Castor bean plants are very poisonous. The poisons are ricin, a toxic protein, and ricinine, an alkaloid. When ingested the beans will cause serious symptoms from nausea, convulsions, coma and death.

Like most of us I don’t often think about whether the plants in my garden are poisonous, but I just read a startling statistic from the 2015 Annual Report by the National Poison Control Center that “plants were implicated in over 28,000 cases of poison exposures.” That statistic is a warning that if we have pets or young children we should be aware of the level of danger of some of our favorite plants.

Rhubarb only eat the stalks
Rhubarb – beautiful foliage but the leaves are poisonous

The list of plants that will cause illness and death is much longer than I imagined. I knew that rhubarb leaves were poisonous and should not be eaten, and all parts of the beautiful datura are dangerous causing hallucinations, delirium convulsions and even cause death. Foxgloves are so toxic that even the water left in a vase holding a foxglove bouquet is toxic. Poisonous plants  surround us.

If you are a reader you may recall that water hemlock, Cicuta maculata, played a vital part in A Thousand Acres by Jane Smiley. Water hemlock is considered the most toxic plant native to North America.

Delphiniums and foxgloves are poisonous plants
Delphiniums and foxgloves are among the list of beautiful and poisonous plants

All parts of several familiar and common plants like delphinium, foxglove, lily of the valley, daphne, monkshood, azaleas and rhododendrons are toxic and if taken in sufficient quantity can sometimes cause death.

I am fascinated that many creatures are aware of plant poisons and know they must not nibble on them. I got all excited when I was told that rhodendron flowers were toxic to honey bees. I had just planted three rhododendrons! But just in time I learned that bumblebees love rhododendron flowers and that the honey bees had zip interest in them. I can relax and enjoy my rhodies, knowing that visiting pollinators are safe. I don’t think there is anyone else of my acquaintance who might be tempted to nibble at the flowers or the foliage.

Rhododendrons – avoided by honey bees but delighting bumblebees

While we should all be aware of the toxicity of the plants in our gardens, I do not think we need to avoid these plants, we just need to be aware of the dangers. I don’t have children in my garden anymore, nor do I have pets. The squirrels and rabbits who visit must take their chances, but I actually think they are much too smart to eat anything that would upset their little stomachs.

Some houseplants are toxic as well.  Cyclamen, spathiphyllum, philodendron, kalanchoe, pothos,  and scheffleras are all dangerous for cats. Bouquets can sometimes be toxic. Lilies are highly toxic to cats who might nibble on the petals, stamens or even the roots after they knock the vase over.

You can go online to find out about the toxicity of garden plants. Cornell has a database listing poisonous plants that can hurt livestock and other animals like humans at I can tell you that the AMA Handbook of poisonous and injurious plants by Kenneth Lampe published by the American Medical Association and The Handbook of poisonous and injurious plants by Lewis Nelson are both available through our local library system.

Wicked Plants by Amy Stewart
Wicked Plants by Amy Stewart

One of my favorite garden writers is Amy Stewart. An early book she wrote is titled Wicked Plants: The Weed that Killed Lincoln’s Mother and Other Botanical Atrocities. This fascinating book tells the story, among others, that you don’t even need to eat a certain plant to have it kill you. Nancy Hanks, Abraham Lincoln’s mother, didn’t eat the Eupotorium rugosum that caused delirium, tremors, weakness and ultimately death. It was the cow she milked that ate the white snakeroot making its milk poisonous. In 1818 when Hanks died Abraham Lincoln was only nine years old. Milk sickness was not an unheard of ailment. It was a problem for cows, as well as for those who drank their milk. Areas where the weed grew in pastures even came to be called Milk Sick Ridge and Milk Sick Holler. It was not until the 1920s that the cause of milk sickness was identified.

Stewart’s book is organized by the types and severity of poison plants from Deadly and Dangerous to Painful and includes the plants are Destructive for the way they can spread and play havoc with the environment. Purple loosestrife and Caulerpa taxifolia, a killer algae are just a few examples.  C. taxifolia is considered one of the worst invaders by the Invasive Species Specialist Group. There are many ways a plant can become dangerous and deadly.

Enjoy your gardens, but beware!

Between the Rows   March 10, 2018

This Post Has 2 Comments

  1. Peter Herpst

    In their defense, wicked plants have a variety of uses. For instance from digitalis is derived a cardiac drug. Brugmansia and other related members of Solanaceae contain important alkaloids such as scopolamine, hyoscyamine, and atropine which have proven medical value for their spasmolytic, anti-asthmatic, anticholinergic, narcotic and anesthetic properties. Some mushrooms are edible, even delicious, while others are quite poisonous. Most of the synthetic drugs we ingest, including yew-derived chemotherapy drugs, came from plants. In addition, plants can be used as natural deterrents for pest insects. What a wonderful and interesting place the garden is!

  2. Pat

    Peter – You are absolutely correct. A retired doctor friend of mine responded to this post. “Paracelsus said: ‘All substances are poisons; there is none which is not a poison. The right dose differentiates a poison and a remedy. . . . Paracelsus was Theophratus Phillipus Aureolus Bombastus Von Hohenheim (1493-1541), a Swiss physician. He became “town physician and professor of medicine at Basle…He defied the authority of Galen and Avicenna, condemning all medical teaching not based on experience….””

    Second, another physician (William Withering) was the first to use the ‘poison’ of digitalis purpurea’ in the (successful) treatment of heart failure accompanying atrial fibrillation, in the 18th. century. In his Edinburgh medical school MD thesis, he also recorded the effects of giving too much – which included GI symptoms and yellowing of one’s vision (the latter of which, I have seen one case!); thus demonstrating the truth of Paracelsus 200 years later.”

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