DANGEROUS

STOP AND SMELL THE RAGWEED

A poisonous seed will only kill you if you chew it and swallow. A painful rash can only spread if you brush up against the leaves. But some plants have figured out how to extend their reach by releasing highly irritating allergens into the air.

There’s a reason why seasonal allergies seem to get worse every year. Gardeners and landscapers, in an attempt to be tidy, prefer to plant male trees and shrubs. The females drop fruit, leaving a mess all over the sidewalk or the lawn. But a male tree produces only small, well-behaved flowers—that is, if your definition of well behaved includes spewing plant sperm into the air for weeks on end.

In the 1950s and 1960s diseased American elm trees were replaced with male varieties of wind-pollinated trees. As a result, some cities, particularly in the Southeast, are virtually uninhabitable for people with serious allergies and asthma.

Homeowners are surprisingly reluctant to remove these trees. One allergen expert remembers a family with a huge male mulberry tree in their garden. After blasting the tree with a hose in a misguided attempt to wash off the pollen, both the husband and wife felt their throats close and had to lock themselves in the bathroom all night just to be able to breathe. The pollen had germinated in water, releasing even more allergens than before.

Consider banishing these plants from the yard:

A versatile weed that flourishes throughout the United States and across Europe. A single plant can produce a billion grains of pollen during a season. The pollen remains airborne for days and can travel several miles, affecting some 75 percent of allergy sufferers and creating cross-allergies with foods that have similar proteins, including cantaloupe, banana, and watermelon. Ragweed releases more pollen when carbon dioxide levels are higher, so global warming will only make the situation worse.

A shrub or small tree popular as a street tree or as a foundation plant in landscapes, this plant is a heavy pollen producer, and the fact that it is often planted right under windows in suburban landscapes means that allergy sufferers may wake up with a sore throat that will only get sicker if they spend the day in bed.

A controversial landscaping tree that can be invasive and cause a nasty skin rash. The berries are poisonous if eaten. The male trees send copious amounts of pollen into the air over a long blooming season. Because it is related to poison ivy and other members of the toxicodendron genus, people who are especially sensitive to those plants will also suffer around pepper trees. It produces an oil that can vaporize into thin air, causing people to develop asthma, eye inflammation, and other reactions just from being nearby.

Olive pollen is so highly irritating, owing to the number of different allergens it contains, that some cities are trying to banish the tree entirely. The city of Tucson, Arizona, has passed an ordinance banning the sale or planting of olive trees.

One of the most potent sources of spring allergies, this plant sheds billions of pollen grains that linger on patios and get tracked indoors.

A fast-growing cedar reaching up to eighty feet tall and forty feet wide, found in gardens and parks throughout mild winter areas in North America and Europe. The small, male cones shed pollen in the fall. Many seasonal allergy sufferers are sensitive to cedar, making this an unbearable tree to be around.

A popular, showy shrub in North America, Europe, and Australia. The long, bristlelike red stamens release golden pollen from the tips. The pollen is triangular in shape and lodges in the sinuses, making it a particularly vicious allergen.

This evergreen is a serious but overlooked source of allergens. The males produce cones, along with large quantities of pollen. Some junipers have both male and female organs on one plant (monoecious), which means that they might produce some berries but will also shed pollen.

One of the most popular grasses for lawns in the South and warm-weather climates throughout the world, it is also the most allergenic. It blooms steadily, and the flowers often grow so low that lawn mowers miss them. New varieties don’t produce any pollen at all, but older varieties are so problematic that some cities in the Southwest have banned them.