The scratchy feeling in the back of your throat, the red, watery eyes you incessantly rub, the sniffles, sneezing and congestion lulling you back inside your house… These are the symptoms of Spring for many of us.

Seasonal allergies or “allergic rhinitis” is most often due to pollen from the plants and trees gracing your property or neighborhood.

Like myself, the average sufferer lives in urban areas. (I have vivid memories of my brother and I performing our garden chores as young teenagers in a postage sized Brooklyn garden – spade in one hand, tissue in the other, sneezing as we work.)  

A brief history -- in 1959, less than 5% of the general population suffered from allergies. That number rose in 1985 to 15% of the general population. By 2000, 38% of the general population in the United States suffered from allergies. * The April 2011 Scientific American suggested that half of all asthma cases have an allergic component.

For a condition that millions of people struggle with, there is unfortunately a lack of interpretation ascribed to this dramatic rise. Theories include the familiar "hygiene hypothesis" that over-sanitizing a child's environment can lead to decreased disease resistance. Others suggest that the rise in allergies and asthma may be due to an increase in airborne pollens, climate changes that trigger a rise in pollen levels, energy-proofing of indoor home and work spaces, urban air pollution, and/or the overuse of antibiotics.

Thomas Leo Ogren, a well-known horticulturist approaches the issue from a new perspective. Three of his books detail the exponential rise in allergies. His latest offers suggestions on allergy-free gardening for designing and installing a large residential landscape design to a small garden design.

Ogren states that eighty years ago “most landscape plants were propagated by seed, and therefore male and female plants in the landscape were roughly 50-50. In the 1940’s the USDA started to recommend growing separate sexed trees from cuttings, budding or grafting with only male wood. According to the USDA this would result in litter free plants as male plants make no seeds, seedpods or fruit to fall on public sidewalks and create a mess.”

Within the nursery trade this balance has now been altered.  Fault does not necessarily lie in the nursery trade, as they are producing to the demand of the buyer.  Landscapers, landscape designers, landscape architects have grown fond of using male trees. Municipalities and homeowners have requested these male trees.

Municipalities, most homeowners and landscapers consider this female byproduct to be "litter" and they don't like to see it lying on sidewalks or in their gardens.  A good example of this would be the Honey Locust (Gleditsia triacanthos). It is one of the most commonly planted trees in urban cities, specifically in street pits.  In nature this tree always has both sexes on the same tree and it also always has many long seedpods. Almost all of the Honey Locust trees sold now are "seedless." They are for the most part litter-free trees." 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.

Remember, ask for female trees.  They trap pollen and clean the air around you. 

Ogren attributes many of our allergies to these gradual changes in our landscapes, the planting of male trees and shrubs.  By manipulating our ecosystem without fully understanding the complexity or the consequences other than from a maintenance standpoint we have created a great public health epidemic. By avoiding messy fruit from female trees, we end up as a result with more pollen, because disproportionate cultivation of all-male plant varieties produces large amounts of intensely irritating airborne pollen.

In nature separate-sexed plants usually occur about 50% of the time. They are dioecious, meaning that there are different sexes among a specific plant. 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.

Most pollen comes from male trees. You might see them advertised as "seedless" or "fruitless." To breathe easier, plant a female tree that won't release pollen. And not all female trees drop fruit. It could be argued that female plants do more to cultivate our ecosystem than males. Because of the way they’ve evolved, female plants trap pollen, lots of it, and they are in effect nature’s finest air cleaners.

Ogren also advocates “sex-changes in trees”—grafting a female top onto existing trunks of male trees. He has also developed and advocates using his Ogren Plant Allergy Scale (OPALS), rating plants from 1 (low) to 10 (high) for pollen and allergies.

In Canada, city planners from both Edmonton and Toronto are now using OPALS to plant more allergy-friendly city landscapes.

In our urban landscapes we now have the most manipulated city forests ever seen. Female trees and shrubs do not produce any pollen, ever, but they do produce seeds, fruits, old flowers, and seedpods.  Flowers on female plants produce much more nectar than do male flowers, and are wonderful for hummingbirds, butterflies, bees, et cetera. The fruits and seeds, produced by female plants feed large numbers of native songbirds. These same birds eat up large amounts of insect pests, leaving the whole garden much cleaner, and with considerably less mold.

*American College of Allergy, Asthma and Immunology