This week’s article sounds like a summer crime thriller, doesn’t it?
Oh, come on. Doesn’t it?
As a landscape designer, my life is pretty calm, so the thought of writing about the garden as antagonist is pretty exciting. Imagine a scene where an unsuspecting gardener in his sun hat and garden gloves is seduced by the beauty of a poisonous plant that appears to be a pea. He nibbles a pod. Its sweet and delicate flavor is intoxicating.
The music becomes ominous and toxins suddenly course through his veins. He falls to the ground, dropping his trowel, convulsing as this plant, this source of toxic beauty and wonder, takes over his body. His breathing becomes ragged and eventually stops. We see his body lying there in the garden, sun shining, quiet except for the birds chirping. A butterfly floats by as if nothing has happened.
Alas, writing about poisonous plants in the garden is about as exciting as my life gets.
Actually, the subject of poisonous plants comes up quite often in conversations with landscape design clients, especially when young children or pets are involved. Although it’s impossible to give you a comprehensive list of poisonous plants in this article, my goal is to provide enough resources to help you find lists of poisonous plants specific to your area.
You can’t determine whether or not a plant is poisonous if you can’t identify it, so be sure to check out my article on plant identification guides and garden books.
Finding Lists of Poisonous Plants
As is typical of a lot of garden information, the best place to find a list of poisonous plants in your area is through your cooperative extension. Simply search the Internet for your state or county with the words “cooperative extension” and “poisonous plants,” and you will usually find what you’re looking for.
The weed control boards of each state will also have lists of poisonous plants. Many plants are considered weeds simply because they are poisonous and toxic to humans and livestock. Locoweed, for example, is toxic to horses and livestock and is problematic when it invades pastureland.
The USDA Agriculture Research Service Plant Research Laboratory has one of the best lists of poisonous plants. They provide lists of poisonous plants organized by toxic syndrome. On this list you will see many common weeds as well as well-known garden plants. Often these plants are listed because they are toxic to livestock or because, if they are allowed to invade farmland, their seeds can get mixed into grains eaten by humans or livestock.
For example, Ponderosa pine needles, if eaten by cattle, cause pregnant cows to abort their calves. The same toxin, isocupressic acid, is found in lodgepole pine, common juniper, and Monterey cypress. This is less of an issue in gardens where livestock will not come in contact with these trees, but it is something to be aware of if you will be raising sheep, goats, or other farm animals.
Lupine (Lupinus spp.) and Larkspur (Delphinium spp.) are common garden plants which contain alkaloids that act as a neurotoxin, causing neuro-muscular failure, paralysis, and often death. All parts of all of the species in the larkspur genus are toxic.
Finally, the University of Michigan has an amazing ethnobotanical database. Just type in the word poisonous and you get a list of poisonous plants. Not all of the plants on this list are poisonous. Since this is an ethnobotanical database, some of the plants on this list are antidotes for poisons, and some are considered poisonous in large doses.
A Short List of Poisonous Plants Found in the Garden
The plants listed here are in no way a complete list of poisonous plants common to the garden. I have listed plants here first by their botanical names. Because common plant names can differ from region to region, it is an unreliable way of referring to plants. Botanical nomenclature is the same everywhere.
Cornus sericea (Redosier dogwood)
Cupressus macrocarpa (Monterey cypress)
Daphne spp. (Daphne)
Delphinium spp. (Larkspur)
Digitalis spp. (Foxglove)
Equisetum spp. (Horsetail)
Eschscholzia californica (California poppy)
Euphorbia marginata (Spurge)
Fritillaria atropurpurea (Spotted missionbells)
Iris versicolor (Harlequin Blueflag)
Juglans nigra (Black walnut) – bark
Juniperus communis (Common juniper)
Juniper scopulorum (Rocky Mountain juniper)
Lupinus spp. (Lupine)
Kalmia latifolia (Mountain laurel)
Pinus contorta (Lodgepole pine)
Pinus ponderosa (Ponderosa pine)
Podophyllum peltatum (Mayapple)
Sambucus racemosa (Elderberry)
Symphoricarpos albus (Snowberry)
Taxus baccata (Engish Yew)
Taxus brevifolia (Pacific Yew)
Taxus cuspidata (Japanese Yew)
Trillium spp. (Trillium)
Finally, just because a plant is poisonous does not mean it can’t or shouldn’t be used in the garden. As I said, I avoid using these plants if pets or young children are going to be present in the garden, but sometimes, these poisonous plants can serve a good purpose.
For instance, many of the above plants are resistant to deer because of their toxic properties. Deer will leave daphne and redosier dogwood alone in favor of other, more appealing shrubs. If you have trouble with squirrels eating your fall bulbs, try daffodils. Since they are poisonous, squirrels will leave them alone, and your daffodils will come back year after year.
Also remember that often only one part of a plant will be poisonous. For example, rhubarb stems are delicious while the leaves are toxic.
Timing is another factor. Potatoes eaten freshly dug make great fries, but a potato that has turned green contains toxins that can make you sick.
The best advice: If you’re not sure about a garden plant, look it up or ask an expert.