Pollen dispersal tests on typical landscape trees such as oak, maple, birch and poplar have consistently shown that more than 99 percent of the source plant's pollen falls out, lands and sticks, usually within 30 feet of the source plant's drip line. It has been casually estimated by a number of pollen scientists that an allergenic pollen-producing tree in your own yard will expose you to 10 times the amount of pollen as would the same tree planted just down the block. The closer the source, the greater will be the total exposure.
In the spring and summer, and often in the fall too, there is always a certain amount of pollen in the air. We may typically be breathing in several hundred grains of pollen with every breath of air we take. However, if your own yard has some highly allergenic, heavy pollinating trees and shrubs in it, at certain times of bloom you may easily be breathing in several thousands of pollen grains with each breath of air. Directly underneath male mulberry trees (Las Vegas, May 1999) airborne pollen levels have been measured that were over 65,000 grains per cubic yard of air space. Were one to accidentally shake a branch of such a tree, and be close and directly downwind of it, exposure could momentarily easily exceed 1,000,000 grains of pollen per cubic yard of air space.
Planting female trees in your own yard will attract and then trap incoming airborne pollen from males of their own species. We could easily think of female trees as our first line of defense. It is, to me at least, quite incredible that the female stigmas, of wind-pollinated dioecious and monoecious species, produce a positive electrical impulse, and that airborne pollen is itself negative. Thus, of course, the pollen is actually attracted like a magnet, right to the female tree, and rendered harmless as it is turned into fruit or seed. When I first learned of this mutual attraction of the two, I was literally blown away with the wonder of it all. But nature has many such fantastic gifts for us, even if we don't at first discover them.
One resource, "Allergy-Free Gardening," lists hundreds of plants to use that are 100 percent pollen-free. It also contains thousands of common landscape plants which are ranked, 1-10, for their ability to cause (or not to cause!) allergies.
This helpful article was provided by DoItYourself.com community member Thomas Ogren. If you are interested in sharing your do-it-yourself knowledge and know-how with the DoItYourself.com's community, click here for more details.
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