Some blame excessive cleanliness, and yet others blame dirty houses and Women’s Lib. Honestly! A highly respected San Diego area allergist told my brother-in-law that women went to work, don’t clean their houses decently any longer, and as a result there is all this dust and dust mites and the resulting allergies.

            But dust mites are not very common in climates like those of California. Dust mites need high humidity to thrive.

            At any rate it is patently absurd to blame the huge rise in allergies on dust. Do we really have so much more house dust now than before? I don’t think so.

            What we do have more of now is pollen, and especially urban pollen.

            Ask one question: What time of year are allergies the worst and when are they the most common? 

The answer: Spring and early summer, precisely the time of year when there is the most pollen around.

            Separate-sexed (dioecious) Species

In our urban landscapes we now have the most manipulated city forests ever seen. In the past twenty-some years landscapers have grown inordinately fond of using male trees. In dioecious species (separate-sexed) there are separate male trees and separate female ones. Female trees and shrubs do not produce any pollen, ever, but they do produce messy seeds, fruits, old flowers, and seedpods. Landscapers and city arborists consider this female byproduct to be “litter” and they don’t like to see it lying on our sidewalks.

As a result we now have huge tracts of these litter-free or “seedless” landscapes in our cities. What these actually are, of course, are male clones. As males, their job is to produce pollen, and that they do. Even though in many cities we now have less total vegetation than we used to, we have more pollen in our air now than ever before.

Monoecious Species

Many street trees have separate-sexed flowers of both male and female existing on the same tree. This is called monoecious, Latin for ‘one house.”

            With many species of monoecious trees the female flowers will trap a good deal of the pollen from the male flowers. A redwood tree (Sequoia spp.) is a good example of this. However the plant scientists figured out back in the early 1980’s how to sex-out the female parts. They started to develop monoecious trees that had no female flowers.

            A good example of this would be the popular shade tree, the Honey Locust (Gleditsia triacanthos). In Nature this tree always has both sexes on the same tree and it also always has many long (messy?) seedpods.

           Almost all of the Honey Locust trees sold now are “seedless.” They are litter-free trees. Very “clean.” What they really are though, are male clones. Their highly allergenic pollen isn’t turned into seed but instead drifts down on us, causing allergies.

Natural Flowering Systems

In Nature separate-sexed plants usually occur about 50% of the time. Half of them are usually male and half are female. The female plants catch pollen from the air, remove it from circulation, and turn it into seed. Female trees are nature’s pollen traps, natural air-scrubbers. The stigmas of flowers on pistillate (female) dioecious trees are actually electrically charged positive (+) and airborne pollen from the males of these same species carries a negative electrical charge. The pollen from the male does not get to the female by accident. Nature designed these to be mutually attractive.

In our modern cities though, female trees and shrubs are rarely used any longer. Of the five most available street trees for sale now in the United States, four of the top five are staminate cultivars, i.e., male clones.

            We recently read in many major newspapers that in the Third World countries, that there are some one hundred million plus missing females. Missing female people. They are ultra sound testing pregnant women and if found carrying a girl child, they are aborted. Clearly females are undervalued.

            It is interesting to see that in modern landscapes the incredibly important female plants are also considered less valuable, and hundreds of millions of them too, are missing. Perhaps the world has gone mad.

Effect of Male Predominance in the Urban Landscape

Because no one bothered to consider the effect of the pollen from all these male trees, we now have many elementary schools, ringed with male shade trees, and full of asthmatic children. Pollen counts exceeding sixty-five thousand grains of tree pollen per cubic yard of airspace have been found in elementary school yards. What does this mean? Simply, it means that on these playgrounds, every child there is inhaling several thousand grains of allergenic pollen with each breath of air they take! And people are surprised that childhood asthma is so common now?

            How common is childhood asthma?

            Asthma is now the number one chronic childhood disease in America.

            Those readers as old as I am (54), think back a bit. We didn’t see all these kids with asthma inhalers at school when we were children. Today though, it is common. All too common.

Pollen Dispersal

            In the past “experts” have criticized the concepts of allergy-free landscaping by saying that, “It doesn’t matter what you plant in your own yard. Pollen will just blow in from somewhere else.” Studies were often mentioned where pollen was collected many miles out at sea, obviously far from any pollen-bearing plants.

           What these so-called experts failed to mention is that the closer someone is to the source of the pollen, the more they get. In some ways it is quite similar to second-hand smoke: If someone is smoking a block away from you, yes, some of that smoke might reach you. However, simple common sense tells us that this isn’t at all the same as having someone smoking right next to you.

            A large male tree in your own yard will expose you to more than ten times the amount of pollen as would a similar tree just down the block. In 1972 a meteorologist from New York, Gilbert Raynor, studied pollen dispersal with a field of Timothy grass. Timothy pollen is well known to be especially light and buoyant. Raynor set up pollen traps at close intervals going away from the field. At a mile from the filed he was still trapping some Timothy pollen, BUT, at a half mile from the field more than 99 percent of all the pollen had already fallen out and stuck. Closest to the field, the most pollen was trapped. The laws of gravity do apply to pollen it appears, even to the lightest of it.

               Solutions

           So what are we to do?  In my book, Allergy-Free Gardening, I strongly suggest we embrace the politics of pollen. At least five cities in the US now have some form of pollen control ordinance: Tucson, Phoenix, Las Vegas, El Paso, and Albuquerque.

           We need to do several things and we need to do them quickly.

·         We need city-by-city local ordinances that forbid the further sale and planting of wind-pollinated male clones of trees and shrubs. Enough already!

·         We need to train people in tree grafting so that they can get started changing the multitude of male trees into female trees. Yes, we can give these trees much-needed sex changes and we ought to get with it. This is surprisingly effective and quite easy to do.

·         Our colleges and universities need to start teaching courses on the impact of plant flowering systems on allergy. No student of botany, urban forestry, ecology, medicine, landscape design, architecture, horticulture, parks and recreation, natural resource management, or city planning should graduate without exposure to this material. Education is the key.

·         All landscape plants for sale in nurseries should be required to have a numerical allergy rating on each container. OPALSä already exists and needs to be used. With this system: 1 = least allergenic, and 10 = most allergenic.

·         We need to ask our elected representatives and ourselves these two questions: 1. How much more allergy is acceptable?

·         2. How many more children need to die from asthma each year before we decide to put an end to these destructive landscape practices?

           I think the answer is obvious. We need to get started now.

About the Author:

Thomas Leo Ogren, the author of Allergy-Free Gardening, has an MS in Agriculture/Horticulture, with an emphasis on plant flowering systems and their relationship to allergy. Tom has taught Landscape Gardening for 20 years, was co-owner of Ogren Brothers Nursery, and hosted the popular “Tom Ogren’s Wild World of Plants” on Public Radio in Minnesota. He is a consultant for the USDA, the American Lung Association, and for www.Allegra.com  Allergy-Free Gardening is his third published book. In January 2003 Tom’s next book, Safe Sex in the Garden, will be published. The Garden Writers of America nominated Allergy-Free Gardening as the one of the “Most Important New Garden Books of 2000.” www.allergyfree-gardening.com

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