With Halloween approaching, October is the season for celebrating things that are spooky, mysterious, and a little dangerous. As it turns out, the garden has its own dark side. Hidden among the flowers and foliage are surprisingly toxic plants, including many we grow without a second thought.
Many plant toxins are essentially a plant protecting itself. Since plants can’t escape predators, they have evolved other ways to defend themselves. Thorns are an obvious example. Tough or unpleasant-tasting leaves are another. Plants are also remarkably sophisticated chemists, producing compounds that can irritate skin, interfere with digestion, or affect the nervous system and heart. In other words, many of these defenses are built right into the plant.
Interestingly, humans have learned to use some of these same compounds to our advantage. Take foxglove, Digitalis. Foxglove contains cardiac glycosides, compounds that affect the heart. Research into these compounds eventually gave us important heart medications, but that doesn't make the plant itself medicine. Eating foxglove can cause nausea, changes in heart rate and rhythm, and, in severe cases, life-threatening poisoning.
Remember, these aren't necessarily unusual plants growing deep in the wilderness. Many are plants we intentionally grow in our own gardens.
One of my favorite plants, lantana, grows throughout my raised beds. It adds a brilliant pop of color amongst my veggies, and the flowers last a long time in bouquets. I’ve always clipped off the berry clusters to encourage more flowering, but while researching this article, I learned those berries and the plant itself can be toxic to pets. Lantana can cause gastrointestinal illness and, in larger amounts, even liver damage. We recently adopted a puppy who will eat just about anything, so discovering that one of my favorite garden plants could harm him was quite a surprise.
Then there is oleander, one of the most familiar examples of a beautiful but deadly plant. Anyone who has driven California's freeways or many spots on our own River Road has seen it. Oleander has been planted extensively because it is evergreen, drought-tolerant, fast-growing, and attractive with its pink, white, and red flowers.
But every single part of oleander is toxic if eaten. The leaves, flowers, stems, and branches contain cardiac glycosides that can interfere with the heart's normal function. Even dried leaves and branches remain toxic, something worth remembering when pruning and disposing of plant material.
Not every toxic plant needs to be eaten to cause trouble.
Euphorbia, a large group of plants commonly known as spurges, produces a distinctive milky white sap when its stems or leaves are cut. That sap can cause significant skin irritation and can be particularly dangerous if it gets into the eyes. One of our community gardeners ended up in the emergency room after getting the sap in her eyes while pruning her euphorbia.
And lantana, oleander, foxglove, euphorbia, and other familiar ornamentals are hardly unusual. Rhododendrons and azaleas, daffodils, hellebores, delphiniums, and many other garden favorites contain potentially harmful compounds. Even the seemingly innocent lily of the valley, with its delicate white bells and famous fragrance, contains cardiac glycosides and is poisonous if eaten.
This doesn't mean we need to fear our gardens or rip out every toxic plant. The more useful approach is to know what we're growing and who may have access to it. A poisonous plant in an ornamental bed may pose very little practical risk to an adult who knows not to eat it. Put that same plant within reach of a curious toddler, puppy, or other pet, and the risk changes.
So this October, while the skeletons and jack-o'-lanterns are out, take a closer look at what's growing in your own garden. Some of the most interesting characters of the season may have been hiding in plain sight all along.
Happy Gardening!