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Avoiding Allergies By Use Of The Right Native Plants In The
By Tom Ogren, Fri Dec 9th
Avoiding Allergies By Use Of The Right Native Plants In The
By Tom Ogren, Fri Dec 9th
Avoiding Allergies by Use of the Right Native Plants in theLandscape Many of our most allergenic plants commonly used in landscapingin the United States and Canada are indeed natives. However, itis the manipulation of these plants by commercial horticulturethat has, and is, causing most of the huge increases we are nowexperiencing with allergy problems. Thirty years ago fewer than10 percent of Americans had allergies. The official figure todayis that a whopping 38 percent of us now suffer fromallergies.(December 99, American College of Asthma, Allergy, andImmunology) Not too many years ago death from asthma was fairlyrare. Today it is all too common and is considered epidemic.Asthma has now become the number one chronic childhood diseasein America. Furthermore, there is new data coming in recentlythat shows a strong connection between over-exposure to pollenand or mold spores and increases in other diseases such as heartdisease, autism, pneumonia, and reflux disease. American Elms The landscape tree in most of America for manyyears was the tall, stately American Elm. The American Elm usedto grace the streets of thousands of towns and cities and whenDED, Dutch Elm Disease, started to spread and kill off thesenative elms, the insect-pollinated, perfect-flowered elms weremost often replaced with wind-pollinated, unisexual-flowered,street trees. Many things happened because of the big switchfrom the elms to these other tree species. First, the elmflowers had a rich nectar source and since these trees bloomedvery early in the season, at a time when insect food sourceswere severely limited urban honeybees and butterflies dependedon this food source. Since the majority of the street trees usedto replace the elms were wind-pollinated, they often lackedthese nectaries and supplied no early-season food source. Soonwe started to see a rapid decline in the total numbers of urbanhoneybees and butterflies. There were other factors as wellbehind this decline, pollution, insecticides, and disease, butthe loss of the crucial early-season food sources should not beunderestimated. DED spread mostly from East to West across theUS and so has the rise in allergy rates. You can actually trackthe spread of allergy from the decline of the elms. The AmericanElms, Ulmus americana, did cause a certain amount of low-level,early spring allergy, simply because they were so very common.The over-planting of elms resulted in a lack of biodiversity andset the stage for the massive kill from the DED. We now knowthat it is always a mistake to use a monoculture, to plant toomuch of just one species. Diversity is always a good idea inhorticulture. (Article continued below)
Diversity Biodiversity
is the way to go when we are creatinglandscapes that will limit allergenic exposure. Almost anyspecies of plants can eventually cause allergies if it isover-planted enough. All to often in our urban landscapes oftoday we see that landscapers have used the same old plants overand over again. This overly simplistic approach to landscapingresults in landscapes that lack originality and produce anumbing "sameness" to far too much of our urbanscape. Whenresidential houses are professionally landscaped with the exactsame plant materials used to landscape banks, real estateoffices, and dentist's shops, we all lose. Allergy rates todayare far worse in urban areas than they are out in the country.Pollen allergies are worse in cities than in the country,despite the fact that there is much more total green matter inthe countryside than in the city. Plant selection has been themain problem. Natives and Urban Landscapes There are many native trees andshrubs used in our landscapes. Maples, oaks, locust, poplars,willows, catalpa, birch, junipers, and many more native speciesare extensively used. Unfortunately the plant breeders andpropagators discovered how to "sex-out" the trees and shrubs.They learned to use only male plants, ironically, as "motherplants," as the source for their scion wood for asexualpropagation. First they just used male plants from the dioecious(separate-sexed) species, but later they learned how to produceall-male clones from species that in Nature were never unisexual(the monoecious species). For example, Honey Locust trees,(Gleditsia triacanthos) are native to our Southeastern US. Lookat these trees in the wild and you will see that all of them arealmost always covered with long seedpods. But go to a nurserynow and look at the Honey Locust trees for sale. The ones onsale now are called "seedless" and they are in effect, all-maleclones. What exactly is the effect of using all male clonedtrees and shrubs in our landscapes? Very simply, this translatesto an excess of allergenic pollen. Only male flowers producethis airborne pollen. Unisexual female flowers produce no pollen. Why the Emphasis on Male Plants? Horticulturists knew thatfemale plants produced seeds, seedpods, and fruit. This "litter"fell on the sidewalks and created a "mess." By using onlyasexually (no sex involved) propagated cultivars (cultivatedvarieties), they were able to create "litter-free" landscapes.These required less maintenance and were (and still are) verypopular with city arborists and the public. In the US today,four of five of the top-selling street tree cultivars are maleclones. Female flowers (pistillate) on female trees or shrubsproduce an electrical (-) current. Their stigmas are broad andsticky. Airborne pollen from male plants has a negativeelectrical impulse before release and a positive charge afterrelease, and this pollen is light and dry. Because of the + and- electrical charges the pollen and the stigmas are drawn toeach other. They are mutually attractive. Mother Nature saw toit that pollen would land, and stick, exactly where it wasneeded. Female plants are nature's pollen traps, our naturalair-cleaners. Today though, most of the female plants are longgone from our landscapes. The pollen from the males floatsabout, seeking a moist, sticky, positive-charged target. Wehumans emit a positive electrical charge, and our mucusmembranes, our eyes, skin and especially the linings of our noseand throat, now trap this wayward pollen. We have become thetargets Allergy develops from repeated over-exposure to the sameallergens. If your own yard is full of pollen-pumping trees andshrubs, you and your family are the ones who will be exposed themost. About the author:Thomas Ogren is the author of Allergy-Free Gardening, Ten SpeedPress. Tom does consulting work on for the USDA, county asthmacoalitions, and the American Lung Associations. He has appearedon CBS, HGTV and The Discovery Channel. His book, Safe Sex inthe Garden, was published 2003. In 2004 Time Warner Bookspublished his latest: What the Experts May NOT Tell You About:Growing the Perfect Lawn. His website:www.allergyfree-gardening.com | Sign In |
