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Creating an Allergy-free Landscape
Thomas Leo Orgen, M.S., Alternative Medicine

Everything is in full bloom-including your allergies. But it doesn't have to be that way. My wife had severe asthma and hay fever, and as a horticulturist, I naturally wanted to create an allergy-free garden to ease her suffering and still beautify the landscape. To my surprise, there was little written on the subject. Years of research in this unstudied terrain uncovered several important factors. Among them, the sex of the plant made a critical difference. Female trees and shrubs in the landscape produce powerful symbiotic effects on local air quality. Here's why the lovely blossoming or fruit-bearing female plants can be good choices.  

The birds and the bees, the flowers and the trees
Many popular species of plants for landscaping are separate sexed (dioecious)Ñthey are individually either male or female. Their different reproductive roles explain why allergy problems begin with the males. Male trees and shrubs shed huge amounts of air-borne pollen-intended to reach the females. But without nearby females, the pollen is unsuccessful in reaching its goal. instead, it reaches your sinuses. Landscaping trends are partly to blame.

Modern landscapes are heavily loaded with male-only trees and shrubs. Among dioecious species are names you will recognize: ash, poplar, willow, cedar, juniper, cottonwood mulberry, osage orange, xylosma, yew, box elder, podocarpus, fringe tree, holly, pepper tree, smoke tree, coffee tree, sassafras, maple and thousands more. The males of these species have been favored by landscapers because they are "litter-free," producing no seeds, seedpods or fruit. What was completely overlooked, however, was the fact that these male plants do indeed produce "litter." Male plant litter is pollen-which is the culprit in a great deal of allergy.

Female trees and shrubs, on the other hand, produce flowers, seeds and fruit, but they shed no pollen. Female-only plants do not have stamens, the male pollen-bearing sexual parts, and so produce no pollen at all.

In nature there is a balance between dioecious males and females, with roughly fifty-fifty of each sex present. urban landscapes, however, the ratio is now usually 90% to 95% male, and 10% or less female. With some urban landscape species, male clones now represent fully 100% of the landscape plants utilized. The result has been instant rise in total urban pollen loads, and corresponding rapid rise in the numbers of people affected with pollen allergies.

Blowin' in the wind
Individual pollen grains are so tiny that they cannot be seen with the naked eye. To view pollen grains individually, magnification of a 1000 power or more is required. They are so small that they easily can pass through the tightest window screens.

Airborne pollen floats around, lands on 17 surfaces, and then becomes airborne again with the slightest breeze. The grains of wind-borne pollen are fight and dry and are negatively electrically charged. Like heat-seeking guided missiles, these tiny, irritating, dry pollen grains-each often shaped like a sharp-spined minute ball of cactus-seek out moist, receptive surfaces.

In spring, summer and even fall in almost any modern city, we are all breathing in several hundred grains of pollen with each breath of air. In some areas people are breathing in thousands of pollen grains with every breath.

The female trees and shrubs that once cleared the air of pollen are no longer used.
Instead, the dry pollen grains land and stick on other moist, receptive surfaces: our eyes, our skin, our mouths, throats and noses, our mucus membranes.

In the sterile, male-predominant modern urban landscape, humans have essentially replaced the female plants, and we ourselves are now the most natural effective pollen traps. It comes as no surprise then that statistics show such a dramatic rise in the number of people affected by allergies to all this free-floating pollen.

Think of someone with allergies as having a large empty glass. Each day into this glass go different allergens-cat or dog dander, dust mites, dust, particulates, mold spores, diesel fumes, smoke-all manner of allergens. The glass starts to get full. Along comes a huge in- halation of pollen and suddenly the glass is not only full, it is now overflowing. Once this happens, the individual gets sick.

We need to limit the total amount of allergens we come into contact with. Avoidance is the real key with allergy. If your own yard has some highly allergenic, heavily pollinating trees and shrubs in it, at certain times of bloom you may easily be breathing in an extremely high number of pollen grains with each breath of air. So the area immediately around your home is an important zone to protect.

Planting female trees and shrubs in one's own yard will help accomplish this. They attract and then trap incoming air-borne pollen from males of their own species. We could think of female trees as our first line of defense.

Other points to consider are diversifying the garden to avoid overexposure to any single species, and paying attention to how highly allergenic different species are, based on their type or amount of pollen. By refer- ring to the OPALS' scale (see sidebar), you can safety select appropriate plantings. Allergist David Stadtner, M.D., noted that everything conventional medicine offers for alleviating allergies has side effects. "The beauty of allergy-free gardening," he wrote, "is that there are no side effects. ItÕs all positive.Ó

Female plants in particular will add beauty to the landscape and abundant rewards for quality of die air and quality of our fives by creating balance in a male-dominant landscape. Since it is overexposure that eventually results in hypersensitivity, diverse plantings also help reduce overexposure to any one type of pollen. The complete OPALS scale is in the book, Allergy-Free Gardening (Spring 2000, Ten Speed Press). Over 5,000 plants are individually ranked.

From the individual to the community at large, there will be many benefits to demanding low-allergy landscapes. Albuquerque, Las Vegas and Tucson have already passed regulations forbidding the planting of some of the most allergenic trees and shrubs. Albuquerque is right now in the process of drafting a model pollen-control ordinance that can be easily adopted by other interested cities.