Almost any substance can be harmful to human health if used improperly. For example, water is essential to our existence, but one can drown in the liquid form, slip and fall on the solid or frozen form, or be scalded by the gaseous form (steam). Plants are as essential as water because they provide for basic human needs such as food, clothing, shelter, and even the air we breathe. And like water, plants also can be hazardous if used improperly. However, our basic knowledge of water hazards is much greater than for plants because water is such a ubiquitous and relatively invariable (water is water, after all) feature of the human experience. Plants, on the other hand, are vastly diverse, and their avoidance of potential hazards is not as deeply ingrained in our psyche. Avoiding the hazards of plants, therefore, requires a practical knowledge of our landscape.

Nightshade, monkshood, foxglove, and poison ivy are among the better known poisonous plants that are justifiably avoided by people who recognize them. Most people are taught at a young age not to touch poison ivy or eat nightshade. But, what makes a plant toxic or poisonous depends on a number of factors. Contact with some plants, such as poison ivy, causes dermatitis or an irritation of the skin. Other plants must be ingested to be toxic. The two most important factors that determine whether a person gets sick from eating a plant are the type of toxin and the amount ingested. Large quantities of almost any food can make us sick. What we don t often realize is that many commonly eaten fruits and vegetables have poisonous parts. It may come as a surprise that apple and cherries have poisonous seeds or that all parts of sunflower plants are "slightly toxic if large quantities are ingested.

It is also important to note that scientists do not typically study the toxicity of landscape plants. Most plants on "poisonous plant lists are there because of strong circumstantial or experimental evidence. Occasionally, however, some plants are erroneously listed as poisonous. One such example is the poinsettia, which is frequently listed as poisonous. However, researchers have found that mice can ingest hundreds of poinsettia leaves or bracts without injury. Although this finding does not preclude human injury from poinsettias, it does propose the poinsettia has been wrongly accused.

Poisonous or toxic plants should be treated with respect. They warrant precaution, not fear. To overcome our fear, we should better understand those plants commonly used in our landscapes and homes. By knowing which plants are potentially dangerous, we can teach our children not to eat them and keep our pets away from them.

Below is a list of common plants that should be appreciated for their beauty, but should not be ingested.

Potential problems with plants in the landscape can be avoided by teaching our children a few commonsense rules:

1. Eat only those plants or plant parts that you know are safe to eat.
2. Identify the plants in your landscape. Check poisonous plant reference to see which plants may be poisonous.

Unfortunately, no list of this type is comprehensive. There will always be potentially toxic plants that are overlooked, so education of homeowners and their children is important. You don t have to remove these plants from the landscape. Usually, their beauty gives us much pleasure and far outweighs their potential pitfalls.

This article originally appeared in the February 21, 2003 issue, pp. 12-13.