MARCH 24, 2009

Some of the plants sold at the Friends School Plant Sale have the “Mr. Yuk” tag on their cards on the sale tables, to identify them as poisonous plants. Here are a few comments from Mr. Yuk, to clarify issues about poisonous plants. These comments refer only to the plants, and not to plants treated with an insecticide, which might render any plants poisonous or dangerous.

These comments do not address allergies to particular plants, medicinal uses of some plants, or tolerances and insensitivities to particular poisonous plants.

What are poisonous plants?

Any type of plant may be poisonous: house plants, garden plants, woody plants or trees. A plant is “poisonous” if it contains a substance that causes chemical injury to something (human or some other animal) that ingests (eats, swallows, licks) or touches the plant. Occasionally, breathing in the scent of the plant or its burned parts can be toxic or irritating. We see this in Minnesota, where burning poison ivy releases the irritant oil, urushiol, into the smoke, causing internal problems for anyone who breathes the smoke.

Are there different types of plant toxicity?

There are three general categories that describe how poisonous plants affect humans and other animals. The time required for development of symptoms varies with the individual poison.

  1. Lethal plants: Some plants are lethal if you eat, lick or swallow the poisonous part of the plant.
  2. Plants that cause digestive problems or pain: Some plants will not kill you, but eating them can make you very uncomfortable.
  3. Skin irritants: Some plants can cause itching, irritation, swelling, rashes.

Are all parts of a “poisonous plant” poisonous?

Plants generally have roots, stems (shoots), leaves, flowers, seeds or bulbs. Whether or not an entire plant or just parts of the plant are poisonous depends on the particular type of plant. In addition, the amount of poison contained in a plant can vary with the age of a plant, the season, and growing conditions. Last, whether or not a plant is poisonous depends on who you are (human adult, human child, or another type of animal.)

Why do plants have poisonous substances?

Plants contain poisonous substances for their own protection — to repel insects and animals that graze on plants.

Do the poisons hurt the plant?

No.

Are human adults and children affected the same way by poisonous plants?

Some plants are toxic to children, but are not lethal or irritating to adults. Because of their physical immaturity, children are more sensitive to many chemicals that do not necessarily cause the same reactions in adults. Remember that there are special formulations of drugs for children, and some medications are OK for adults, but not for children. Dosage is dependent on age, maturity of metabolism, health, weight, and other medications you may be taking. Similarly, plant toxins may affect different people differently.

What about animals?

Different animal species have different metabolisms and different populations of microorganisms living in their guts, which can detoxify some plant poisons, resulting in different sensitivity to plant toxins. For convenience, the plants at the Friends Plant Sale have only been classified with respect to toxicity to humans. If you have questions about animal sensitivities, you should check with your veterinarian.

How can I find out more information?

Many plants have the same or similar common names. This can be confusing and misleading when trying to identify poisonous plants. Latin names are the best way to insure that the information you are seeking applies to the plant you are concerned about. Many poisonous plant databases have plants identified by Latin names and common names, to help you find the plants of interest. Here are several online databases that are easy to use with either the common or Latin name. Remember that just because a plant is not listed, it is not necessarily nontoxic.

How can I garden responsibly with poisonous plants?

  1. Inform yourself about the toxic plants and plant parts on your garden plants. 
  2. Be aware of the population (human adult and child) with easy access to your garden.
  3. Isolate plants that have lethal consequences, so that they are not easily reached by anyone who can be harmed by ingesting them. For example, you might plant monkshood and Datura in the backyard, where casual traffic will not easily encounter these toxic plants.
  4. Choose to plant only edible or harmless plants in the front yard or any place that children will have easy access to these plants.
  5. Because berries can be an attractive nuisance, choose to plant only those species that bear edible or harmless berries. 
  6. Choose to plant nontoxic species that will grow in similar conditions and have similar appearances. For example, if you are planning a rainwater garden, high bush cranberry is a nontoxic alternative to winterberry.
  7. Educate your children. Teach them to avoid eating or sucking on any plant parts until they have been positively identified as safe.

Mr. Yuk, AKA Sara Barsel, Ph.D., is a local scientist, educator, and passionate gardener. She volunteers for the Friends School Plant Sale as Mr. Yuk because she values the plant sale, maintaining healthy life forms, and responsible gardening.