Nursery Market Report: April 2001, Creating Allergy-free Landscapes

Spring has arrived and so has allergy season - a time that many landscape clients dread. This can change by creating allergy-free gardens to ease their suffering while still beautifying the landscape.

The sex of your plants is the most important consideration when creating an allergy-free landscape. Male trees and shrubs shed huge amounts of airborne pollen intended to reach the females. When females are not nearby, the pollen reaches sinuses instead.

Modern landscapes are loaded with male-only trees and shrubs, including ash, poplar, willow, cedar, juniper, cottonwood, mulberry and xylosma, among others.

Landscape contractors favor the male species because they are "litter-free," meaning they produce no seeds, seedpods or fruit. But these male plants do produce "litter," or pollen, which often triggers allergies. Female trees and shrubs, on the other hand, produce flowers, seeds and fruit, but they do not produce or shed pollen.

In nature, there is a balance between males and females, with roughly 50 percent of each sex present. In urban landscapes, however, the ratio is typically 90 to 95 percent male and 10 percent or less female. With some urban landscape species, male clones now represent 100 percent of the landscape plants used. The result has been a constant rise in total urban pollen loads and a corresponding rise in the number of people affected by pollen allergies.

Airborne pollen floats around, lands on dry surfaces and then becomes airborne again with the slightest breeze. Instead of landing on female trees and shrubs, the dry pollen grains often land and stick on other moist, receptive surfaces - our eyes, skin, mouths, throats and noses. Humans are often the most natural effective pollen traps.