When you're designing an ornamental garden, you're usually thinking about how plants look, not how they taste. After all, you're not about to serve daffodils for dinner or pack azaleas in your child's lunchbox. And a very good thing that is, because both azaleas and daffodils are poisonous.

Many ordinary garden flowers are poisonous to people and other creatures. They're not all fatal, but they can cause all kinds of distress.

Did you ever wonder why deer don't eat certain spring-flowering bulbs, such as daffodil, hyacinth, autumn crocus, snowdrop (galanthus) and star-of-Bethlehem (Ornithogalum umbellatum)? It's because they're toxic. Star-of-Bethlehem bulbs brought to the surface in cultivation have been mistaken for spring onions or wild garlic. Eating these bulbs can cause nervousness, stomachache and other gastric distress.

Cherry tree twigs and foliage, both wild and cultivated, contain a compound that releases cyanide when chewed. So don't gnaw on the stick you use for roasting marshmallows. The branches of oleander, which grows wild in California and Florida, are poisonous. Wisteria, foxglove, lantana, morning glory and English ivy are also toxic.

It's important to know which plants are harmful because pets and children can be attracted to them. Children can be drawn to a flower or berry and eat it without realizing it will hurt them. Most adults know not to eat mushrooms they find growing in the wild, but most children don't, so they should be warned about picking and eating them. Of course, planting toxic ornamentals on school grounds, playgrounds or daycare centers should be avoided. Homeowner awareness can help prevent this from happening.

I think that one of the most astonishing toxic plants is daphne. It's a plant collector's dream to have a Daphne odora, which emits a wonderful fragrance that drenches the air when it blooms in late winter. This plant is often found gracing the entries of garden centers in March because its flowers and fragrance are great attention-getters. All parts, though, can be extremely dangerous. The berries are corrosive and will burn your mouth and digestive tract, and even the sap can irritate your skin. Just a few berries can be fatal to a child.

I'm not issuing a blanket warning against planting anything that might be toxic. But you need to warn children not to eat plants from your garden or anywhere else without asking first, and you should keep poisonous plants away from pets.

On the flip side, some plants are toxic to some pests. Therefore, voles, deer, gophers and rabbits will allow them to grow in your garden.

For instance, I would never want to stop planting hellebores. However, it has been known since ancient Greek and Roman times that it is a toxic plant and will cause severe vomiting if eaten. From a design standpoint, it's a useful, low-maintenance evergreen perennial for shady sites. It flowers in winter, has handsome foliage and a long blooming season -- and it's deer-resistant. On the other hand, yew, which has juicy, red toxic berries that can attract children, has foliage so toxic it has been known to kill livestock, but it has no effect on deer.

The ornamental garden is not the only place toxic plants can lurk. Eating parts of potato and tomato plants, except the actual potato or tomato, can cause severe stomach and nervous system problems. And the only harmless part of rhubarb is the stalk.

Some common houseplants also have toxic effects. Among them are aloe, dieffenbachia, philodendron and calla lily. Avoid these if you have children or pets that might try to munch on them. Some common houseplants safe to grow around young children are African violet, begonia, spider plant, Swedish ivy, wandering Jew, snake plant (Sansevieria), weeping fig, dracaena and jade plant.

While we're on the subject of plants that cause distress, one of the most prevalent is poison ivy (Rhus radicans). It has pros and cons.

If you have ever been a victim of the extremely uncomfortable, hot, itchy, burning rash caused by this innocent-looking plant, you already know the cons. But here are benefits of poison ivy. It is a native American plant, a favorite source of food for birds, and superb cover and habitat for many critters that live on the forest floor or in trees. In fact, poison ivy, a close relative of the pistachio and cashew, is not truly poisonous. It's one in a family of plants that produce sap that's caustic to humans. Some people don't react to it, but it can make others miserable, even in small patches.

If the oil stays on your skin for more than 10 minutes, you can get a rash, which sneaks up on your skin over a period of 24 to 72 hours, depending on your level of exposure and sensitivity. Although you have to come into direct contact with the oil or with smoke from burning poison ivy to get the rash, remember that the allergen, urushiol, doesn't become dormant; it remains active for days on whatever it touches, including the family pet. Pets don't get a rash, but they can get oil on their fur and then rub it onto your furniture, your rugs and you. It remains on your clothes if you don't wash them.

Learn to recognize this plant, which can look like a small shrub, or like a vine if it's climbing a tree. Scouts are taught, "Leaflets three, let it be," because the leaves grow in groups of three, usually with a red area in the center where the stems of the leaves meet. The leaves might have smooth edges, be slightly lobed or have an undulating margin. The woody stems are tan and might be covered with reddish-brown, hair-like aerial rootlets if they're climbing a tree or building.

If you have to work around poison ivy, wear gloves, long sleeves and long pants, and keep your socks pulled up. Wash your clothes with a strong soap; as soon as possible, use a solvent, such as such as isopropyl alcohol, to rinse any areas where the plant touched your skin.

To kill poison ivy, carefully cut the stems growing up trees near the ground. When they leaf out again, spray with a glyphosate weed killer such as Roundup or Kleeraway.

If you have an encounter with a plant that might be poisonous, call the National Capital Poison Center at 800-222-1222. It is staffed 24 hours a day, every day.

Joel M. Lerner is president of Environmental Design in Capitol View Park, Md. E-mail or contact him through his Web site, www.gardenlerner.com.