Dorothy is a master gardener, former newspaper reporter, and the author of several books. Michael is a landscape and nature photographer.
Most Poisonous Plants and Flowers Are Harmless When Left Alone
I am the kind of person who likes to touch things. Mike used to get upset with me when we went to flower shows because I always had to touch the plants, never considering that I could be harming them, or worse: they could be harming me. That was back during the days before I became a Master Gardener and began studying plants in depth—the good, as well as the bad and the ugly.
Chemical Reactions Make a Plant Poisonous
I know now that a plant is the product of a series of chemical reactions that produce useful materials like carbohydrates, proteins, fats, gums, resins, and enzymes. Unfortunately, they also produce other chemicals that can adversely affect animals as well as people.
When you learn that a plant is poisonous, take that as a warning. The chemicals in some plants can cause irritating reactions to the human body. Most people already are aware of the dangers of poison ivy, poison oak, and poison sumac, but those aren't the only ones by a long shot that can cause you hours, days, or weeks of misery.
Toxic Plants Can Cause Chemical Changes in Your Body
Some chemicals in plant juices or on the surface of leaves can irritate the skin, inducing blisters, reddening, or swelling. They can also create chemical changes in your body, resulting in sensitivity to light, discoloration, or actual erosion of skin tissue (in extreme cases).
Your Best Protection Is Education
No one can predict the possible human reaction to all plants, so I would advise you to learn which ones have the potential for danger and stay away from them (knowing that most gardeners are probably willing to put up with some slight discomfort to have a beautiful yard).
Although there are many that can cause mild irritation, I am writing this article to expose you to some that could be extremely hazardous to you, your inquisitive children, and your fearless pets.
All Parts of These Plants Are Poisonous
Autumn Crocus (Colchicum cilicicum)
This plant is commonly grown for its showy lavender flowers, which appear in the fall without leaves. Because you can place it on a windowsill and force it to bloom, it can be an object of curiosity to a small child. All parts of this plant are equally and intensively poisonous.
Symptoms include burning pain in the mouth, vomiting, diarrhea, intestinal pain, reduced pulse, coldness of the extremities, and weakness.
Lily of the Valley (Convallaria majalis)
Lily of the valley is a popular perennial garden plant originating from Europe and naturalized in parts of North America. Some cultivars of these strongly perfumed flowers are pink, with variegated leaves. The fruits are red berries with many seeds.
At least 38 cardenolides (steroids) have been isolated from this plant, which also has various toxic compounds (saponins) present.
All parts of the lily of the valley plant (flowers, berries, leaves, and underground portions) are poisonous, with the greatest concentration of cardenolides being in the roots. The beautiful red berries are the most common source of poisoning in children, and the cardenolides have a digitalis-like activity, causing cardiac conduction disturbances.
Daphne Shrubs (all species)
All parts of the daphne shrub are poisonous to both animals and humans. In fact, they are so toxic that merely chewing on the flowers, foliage, bark, or red berries can be fatal. Two or three fruits from a daphne shrub can contain enough acrid juice to be fatal to a child; all parts of every species are highly toxic.
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Vomiting and diarrhea, with blood or mucus, are common symptoms, as well as skin blisters from the juice, and blisters of the soft tissues of the mouth from any plant portions chewed or swallowed.
Common Foxglove (Digitalis purpurea)
All parts of a common foxglove plant contain a number of harmful substances that are toxic as well as deadly. Children often pick the drooping tubular flowers and suck the nectar from their base, but doing so can have serious consequences such as nausea and vomiting, along with a very slow pulse which is followed by an erratic or rapid heartbeat.
Eating any amount of any part of the foxglove plant could make you seriously ill. Always plant foxglove out of the reach of small children and animals.
You should always wash your hands after handling monkshood (also known as aconite, wolfsbane, leopard's bane, mouse bane, women's bane, devil's helmet, queen of poisons, or blue rocket).
All parts of it are poisonous if ingested or if the sap comes into contact with any mucous membrane. The effects range from skin irritation to cardiac and respiratory failure. All parts are toxic, especially the roots and seeds, and the flowers if eaten.
Symptoms of monkshood poisoning may include tingling of the tissues of the mouth followed by numbness; a sensation of warmth in the stomach; nausea (frequently without vomiting); slowing of the pulse and respiration. Death can follow within only a few hours of ingestion.
Mountain Laurel Shrub (Kalmia latifolia)
The mountain laurel is an exquisite flowering shrub with a multi-stemmed growth pattern indigenous to North America (mainly in the eastern half). Unfortunately, all parts of this beautiful shrub are poisonous to humans and many animals, including horses, goats, deer, cattle, and monkeys.
Grayanotoxins (neurotoxins) are present in all parts of the plant including the nectar and affect both cardiovascular and respiratory systems.
Symptoms of grayanotoxin poisoning begin to appear approximately six hours after ingestion. They include a burning sensation in the mouth and pharynx, anoxia, emesis, muscular weakness, salivation, dimness of vision, and bradycardia followed by severe respiratory paralysis, hypotension, coma, and death.
Photos of Poisonous Plants and Flowers
Know What You Are Planting
The plants I have discussed in this article should not be considered a complete listing of poisonous plants.
If you have children or pets you need to do some research before planting anything in your yard to which they might have access. It would be impractical to list them all here because there are so many out there with varying degrees of toxicity.
Some plants can be mildly toxic and just give you a stomach ache if you eat too much of them but others can be deadly. Know the category into which your desired plants fall before you put them in your yard.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
© 2020 Mike and Dorothy McKenney
Mike and Dorothy McKenney (author) from United States on August 27, 2020:
Thanks so much! I have learned much more than I ever thought possible. I appreciate you continuing to read my work.
Dora Weithers from The Caribbean on August 26, 2020:
Wow! You may have saved many of us from problems we did not know exist. Thanks for this important information. How could such a beauty as the lily of the valley be such a problem? There's so much we don't know, which we should.