Poisonous plants may seem a strange topic for a plant lover to write about, but gardeners should not duck the subject. Nothing would take the joy out of gardening like having a child or pet get sick after chewing on a houseplant or something in your garden. With a little knowledge we can avoid bad things happening for nice gardeners.
The logical concept would be for gardeners to refer to a list of poisonous or toxic plants and simply not plant them – but here’s the rub: The list of “poisonous plants” for humans or pets is so long, with so many familiar garden and houseplants on it, that a person could simply give up. Are you really going to avoid chrysanthemums because it’s on some list? Let’s put the lists in perspective.
First, it’s a litigious and cautious world, for some good reasons as well as outlandish extremes. As with pharmaceuticals, warnings and possible side effects must be listed even if the experiences are just anecdotal and evidence is specious. Second, hundreds of plants reach these lists because they simply irritate skin or cause a stomach upset for people or pets who eat a great quantity. Not all “toxins” are equal. The lists often name plants that can kill next to plants that make you itch overnight.
Let’s sort out which plants are seriously poisonous or toxic – we’ll use the words interchangeably here – and should not be planted where people or animals might ingest or handle them. But must a gardener shun every plant ever listed as possibly causing a stomach upset or skin irritation? Let’s make responsible choices based on research and science-based information.
Some individual responsibility is also called for. As gardeners, parents or pet owners, let’s manage pets and children (our own or our guests) so they don’t eat plants that are not intended for consumption. I know that is not always easy. Some cats and dogs (especially puppies) simply chew on the nearest foliage. (Cornell vet school recommends bran flakes or higher fiber in puppy diets). Children put lots of things in their mouths, especially berries. One poisonous plant researcher advised us to consider children “as grazing animals.”
Degrees of danger
Predicting or diagnosing reactions to plants is a messy business. Individual response to allergens fluctuates wildly and can change as one ages. Susceptibility and responses to internal poisoning also varies among individuals. Children or small people react differently from larger people, and it makes a difference whether a stomach is full or empty. Even when plants are well known as toxic, their degree of toxicity differs with the part of the plant that’s consumed, the time of year, age of the plant, and even where the plant is grown. Green or sprouting potatoes could make you sick, but you’re not giving up potatoes.
Common sense and familiar generalities don’t help much in figuring out what’s toxic, either. Just because a plant tastes bitter does not mean it is dangerous. Just because a plant is safe for cattle or goats to eat doesn’t mean it’s safe for horses or people. Birds eat many berries that humans cannot. Plants can’t be judged by their botanical families, since many beans, seeds, roots or greens are edible while having very nasty relatives. Traditional wisdom also misleads: Many indigenous people or herbalists know how to harvest or prepare some poisonous plants to use as food or medicine – but that doesn’t mean we should start eating or using the plant without full knowledge.
Understanding toxicity is complicated.
Some of the most dangerous plants
This information is based on lists and reports from Cornell University, the ASPCA and Humane Society, and several books on poisonous plants. But I am not a doctor or veterinarian. Contact your physician or vet if you suspect poisoning. Also do your own research before you re-design your garden.
Poisonous to humans
These are some of the most potentially toxic plants:
• Pokeweed: all parts poisonous; purple berries could tempt children. There’s also Southern lore about “poke salad” (made from very young leaves, cooked). Avoid.
• White baneberry (Doll’s eyes): All parts poisonous.
• Bittersweet nightshade: Toxic weed with multi-colored berries. Remove.
• Yews (Taxus): Ubiquitous landscape shrub. All parts, especially the seeds within the berries, poisonous to humans, horses and others.
• Castor bean: Ornamental annual; seeds contain ricin – potentially lethal.
• Angel’s Trumpet (Brugsmansia): Hallucinogenic, toxic, and may cause dermatitis.
• Monkshood, wolfsbane (Aconitum): Contains alkaloids. One of the most deadly perennials if ingested; can even poison through a cut in the skin.
• And more: Foxgloves, delphiniums, white snakeroot (Eupatorium rugosum) and rhododendrons can also poison.
Just don’t graze in the garden!
Poisonous to pets
The following are poisonous to cats and dogs, unless just one is named. If you see excessive drooling, vomiting, diarrhea, weakness, diarrhea or labored breathing, get your animal to the vet – and take the suspected plant and its name with you:
• Aloe vera: fixes burns but poisonous to pets.
• Amaryllis: especially the bulb is toxic.
• Azaleas and rhododendrons: toxic to all pets including horses, goats, sheep.
• Baby’s breath: causes vomiting and diarrhea.
• Begonias: can cause vomiting, drooling, diarrhea, intense burning in the mouth.
• Ivies: ingesting foliage causes gastric symptoms.
• Lilies: Extremely dangerous for cats, causing kidney failure, even after ingesting small amounts of the leaves. Lilies don’t hurt dogs. Includes all Lilium (Asiatic, Easter, Oriental etc.) but doesn’t include Daylilies.
• Morning glory: Causes severe agitation, disorientation, hallucinations.
• Oleander: Tropical plant, severely poisonous, even leading to cardiac failure in people, pets, horses and more.
• Sago palm: Landscape plant in temperate regions; common bonsai plant indoors. Cats like to chew it – highly toxic to many mammals.
• And more: Eating milkweeds, carnations, chrysanthemums, and hostas can make pets sick. Chewing lots of daffodil bulbs or gladiola corms would be dangerous, however unlikely.
Just keep an eye on Fluffy and Fido, and watch what they’re tempted to chew.
Many plants also cause dermatitis, sometimes severe – topic for another day. Only you can decide what plants to grow and keep, depending upon the people and animals that have access. Keep learning and be careful.
Sally Cunningham is a garden writer, lecturer and consultant.