‘It’s a mistaken idea that animals know what is poisonous. . . . Unfortunately, a number of pets are poisoned by plants, and the diagnosis is missed because the unsuspecting owner doesn’t realize the pet has ingested a toxic plant.
Pets can wreak havoc with a garden. And vice versa.
Numerous plants, including many natives and so-called weeds, can be harmful, even fatal, to companion animals, and pet-loving gardeners must know which ones they are.
“The No. 1 problem plant for toxicity in this region is oleander,” said William Emboden, a professor of biology at Cal State Northridge and the author of numerous botany books.
“Every part of oleander is toxic, even when dried, and ingesting just one leaf can even kill a human,” he said.
Oleander is a common sight in Southern California because the drought-tolerant plant is widely used as a hedge. While small animals usually leave it alone, there are many cases of horses and cattle eating oleander.
“Daturas are another species which is deadly, and should be treated with extreme caution,” Emboden said.
Evergreen shrubs that can be trained to grow as small trees, daturas are also known as Angel’s Trumpet or Brugmansia and are closely related to the native California annuals or perennials, jimson weeds.
The large tubular flowers, usually white, are highly fragrant and very poisonous.
“One variety, Datura inoxia, a perennial herbaceous shrub, is the most dangerous because the velvety leaves contain toxins at the surface,” Emboden said.
“An animal, or human, can be affected just by touching their leaves. Cats, which would not normally eat this plant, can be harmed just by walking by and brushing the leaves.”
Research during the past decade has revealed that many plants have developed the ability to deter insects and herbivorous animals from munching on them by developing toxins. In this co-evolution process, the animals have developed methods of detoxification to protect themselves from the toxins in the plants they do consume.
However, dogs and cats haven’t developed these self-protective mechanisms, and puppies and kittens, particularly, are at great risk because they explore their world with their mouths.
“So many hundreds of plants can be toxic, and as a rule, puppies are more aggressive and less discriminating about what they eat, so they’re usually at risk,” said Dr. Francis Galey, a specialist in veterinary toxicology at UC Davis. “They will chew on seeds, bulbs, branches, pits, and even leaves.”
“Plant toxicity varies according to the season. We get a number of calls at Christmas because mistletoe and holly berries are deadly to animals and too many people don’t know it.”
He added that some plants have an undeserved reputation for toxicity.
“For years, poinsettia has been labeled as toxic, but latest research has shown that the plant it not highly toxic. However, it does cause vomiting in the animals that eat it and for that reason pets should be prevented from access to it,” he said.
Galey also pointed out that pet owners sometimes become confused when they see their pet eating a plant and then vomiting, mistaking an effect for the cause of pet poisoning.
“Since dogs and cats will try to ingest grasses or other greenery if they have gastrointestinal upsets, which cause them to vomit, the unknowing pet owner may think the plant has caused the vomiting when in reality it didn’t,” he said.
“It’s always best to be cautious and check with a veterinarian.”
There is a widely held--but erroneous--belief that animals possess a native wisdom or intuition that keeps them from eating poisonous substances.
“It’s a mistaken idea that animals know what is poisonous and won’t consume anything that is,” said veterinarian Christopher Cauble, who operates Mobile Vet and treats his animal patients in their home environment.
“Unfortunately, a number of pets are poisoned by plants, and the diagnosis is missed because the unsuspecting owner doesn’t realize the pet has ingested a toxic plant,” he said. “Because I see the animals in their own homes, it’s possible to determine if the animal is sick because of what it consumed.”
Recently, he was called to euthanize a Great Dane dying of kidney failure. The dog wasn’t responding to medication, and the underlying cause of the kidney failure couldn’t be determined. The owner didn’t want to see his dog suffer any longer.
“When we were in the garden, deciding on the most suitable spot for burial, I spotted large quantities of pigweed and questioned the dog’s owner why it was growing there,” Cauble said.
“He explained that the dog had enjoyed chewing on the plant, and I knew that was the source of the problem. The plant contains toxic amounts of oxalates that form crystals in the dog’s kidneys. Unfortunately, it was too late to cure him.”
Charla and John Hutcheson were more fortunate.
They live in Arcadia near the Los Angeles County Arboretum, and their garden was overrun with gophers. They decided to plant gopher spurge, a type of euphorbia. It did rid their garden of gophers, and almost killed their 3-month-old Tibetan mastiff.
“Because Maharenee chewed everything she could, I didn’t permit her in my garden alone,” Charla Hutcheson said. “I was outside with her, and just took my eyes off her for an instant. She consumed half a gopher spurge plant before I could stop her. I was uneasy for two days since I knew the plant caused hemorrhaging in gophers.
“Sure enough, in just a few days I saw her bloody stools and summoned Dr. Cauble to treat her. Fortunately, since we knew the reason for the problem, we medicated her and saved her life. But I was annoyed that the mail order company that sells this plant claims it won’t harm domestic animals. Obviously, that’s not true.”
Since the Hutchesons still needed the gopher spurge to protect their garden, they protected Maharenee by building an enclosed patio in which she was confined when she wanted to be outside.
Toxicity in plants is complicated by the fact that not all parts of the plants may be toxic, or they may be toxic just at certain times of the year. The amount consumed is also relevant, for with the exception of oleander (Nerium oleander) and castor beans (Ricinus communis), one bite is rarely fatal.
“If a pet owner suspects plant poisoning, it’s best to rush the animal to the family veterinarian or local emergency pet hospital,” advised Dr. Barbara Hook, a certified veterinary toxicologist with the Los Angeles County Veterinarian’s Office.
“People should be aware that there’s a big difference between animal and human systems, and some surprising things are poisonous to pets. For example, onions can be deadly to animals and, of course, are safe for human consumption.”
She also suggested that if at all possible, the pet owner should take a sample of the vomitus to the veterinarian. “The sample will usually contain the ingested plant, and the vet can save valuable time by seeing what actually made the animal sick,” she said. Take the plant as well for identification.
Although dogs and cats are the most common companion pets, other pets such as rabbits, birds and turtles should also be safeguarded from plants that are labeled as toxic. While hundreds of plants are considered toxic, the following are the most likely to be found in Southern California:
Azaleas and rhododendrons (Rhododendron spp.)-- Large quantities of the green leaves must be ingested before lethal poisoning occurs.
Boxwood (Buxus)-- These evergreen shrubs are widely used for hedging and edging. All parts are toxic.
Castor bean (Ricinus communis)-- The seeds are very toxic and just two can kill a human. Since only the seeds are toxic, this popular, fast-growing shrub can be safely included in the garden by removing the flowering head from the plant.
Datura--also known as Angel’s Trumpet. All Datura species are poisonous. Jimson weed (Datura stramonium) is an abundant native of this region. Its seeds are most likely to cause toxicity in pets.
English Ivy (Hedera helix)-- Although both the foliage and fruits are toxic, the poisonings reported have been from the fruits.
Heavenly bamboo (Nandina domestica)-- The leaves contain cyanide.
Larkspur (Delphinium)-- All species of larkspur and delphinium should be considered poisonous. The plants are most toxic in their early growth and seed stages.
Monkshood (Aconitum napellus)-- Also known as wolf bane, it was cultivated in Europe for centuries and used to poison wolves.
Oleander (Nerium oleander)-- Because oleander is bitter, animals rarely eat it. But puppies and kittens may be at risk if allowed to play among its dried leaves.
Ornamental tobacco (Nicotiana)-- Nicotiana is a fragrant flowering ornamental in the tobacco family that, although toxic, rarely causes death in the animal ingesting it because the nicotine is absorbed slowly in the body.
Oxalis--There are many varieties of this low-growing perennial, and one is such an aggressive grower in this region that it’s considered a weed. All species contain oxalates.
Pigweed (Amaranthus spp.)-- A member of the Amaranth family, grown for ornamental leaves and grain, Pigweed is considered a weed and contains oxalates.
Purple foxglove (Digitalis purpurea)-- the leaves are poisonous.
Spurges (Euphorbiaceae)-- Besides gopher spurge, other types of euphorbia are poisonous. Perhaps the most widely known is poinsettia. Its milky sap irritates skin and gastrointestinal tracts of puppies, kittens, and birds.
Yew (Taxus spp.)-- Both the foliage and twigs are toxic.
Additionally, many popular garden ornamentals are grown from bulbs or corms, and these can be poisonous. The bulbs of tulips, daffodils, amaryllis and iris should be stored and planted where pets can’t have access to them.
New research reveals that feeding avocados to birds, rabbits and cats can cause severe toxic reactions, and even death in birds. Apricot and peach pits contain cyanide, and pets should never be allowed to consume them.
Some vegetables too can be toxic to animals. These include spinach, rhubarb stalks, potato vines, onions and tomatoes.
One of the main reasons poisoning by plants goes undetected in companion animals is that it’s difficult to diagnose by symptoms alone. Different plant toxins affect the gastrointestinal system, the nervous system, or the circulatory system.
Also, pets are poisoned more often by insect or rodent poisons than they are by plants.
But with careful planning, it’s possible to enjoy gardens and pets without harm to either. Know what you grow, and as a general precaution, don’t permit pets free access to a garden containing any plants that can be potentially harmful to them.
Toxic Plants in the Home
Some houseplants can also be toxic. Kittens and cats confined indoors are at risk because they’re likely to chew plant leaves when they’re bored, playing or even teething. Puppies will also consume plants, in addition to other prized household items.
Pet birds will also spend a good deal of their time chewing, tasting and nibbling. If they have access to plants, they’ll include them in their explorations.
The following houseplants are considered toxic: Cutleaf philodendron, dieffenbachia (dumb cane), elephant ear (taro), eucalyptus (dried or partially dried, which are dyed or chemically treated for flower arrangements), holly, mistletoe, philodendrons, poinsettia and pyracantha.
LEARN MORE ABOUT POISONOUS PLANTS Sources for listings of poisonous plants:
“Plant Poisoning in Small Companion Animals” by Murray E. Fowler, published by Ralston Purina Co.
“Poisonous Plants of the United States and Canada” by John M. Kingsbury, published by Prentice Hall Inc.