EDMONTON — As people with pollen allergies (sniff) already know, botanical sexism is alive and growing.

Most North American cities plant more male bushes, trees and plants than their female counterparts. They do this because pollen-producing male trees don't bear fruit or make seeds that drop on the ground the way female trees do.

The mess the females create can clog drains and create sewage problems, cause people to slip and fall — the city would be liable for injuries — and attract wildlife and wasps.

The sexual imbalance makes for a cleaner-looking city, but it also creates a pollen-saturated environment, says California horticulturalist and author Thomas Ogren. All this pollen causes a sensitivity in people that can eventually lead to an allergy and this, he says, partly explains the rise in urban pollen allergies.

Seasonal allergies, also known as hay fever, are very common, affecting about 15 per cent of the population, says Dr. Harissios Vliagoftis, an allergist in the University of Alberta's Department of Medicine and a board member of the Lung Association Alberta & NWT.

Ogren is right that allergies have been increasing over the last 15 to 20 years in developed countries, he notes. There are several immunological theories as to why, including the hygiene theory, that our immune system doesn't get stimulated enough when we're young because our environments are too clean.

"Because of that, our immune system doesn't learn how to respond correctly to all the external stimuli and that's why allergies develop," Vliagoftis explains.

Under that theory, Ogren's case against planting less-messy, all-male trees, makes sense, the allergist says.

"I don't know how much things would change if we change the way we plant trees because there is not very good data on how much pollen you need to get sensitized, but during the times of year when pollen counts are high, (and male trees make pollen), allergic people do have more problems," Vliagoftis says.

Yet none of the 10 Canadian cities Ogren's researched and plans to visit this spring — including Edmonton where he arrives on March 30 — takes this into account when landscaping, Ogren says.

Jenny Wheeler, the city's principal of forestry, was allergic to blooming sage brush when she lived in Medicine Hat, Alta., so she understands what it's like to have a hard time breathing because of pollens. But people have to learn to live with nature, she says.

Ogren, a past consultant with the U.S. Department of Agriculture and author of several books including Safe Sex in the Garden and Allergy-Free Gardening, says there's a better solution: plant more (single-sex) female trees to attract the pollen produced by males, or plant trees with both male and female parts, since the pollen doesn't spread as much.

A growing number of American cities have pollen-control bylaws that forbid the sale or planting of certain plants and trees, he notes, after a six-year-old boy playing with friends at a zoo in Albuquerque, N.M., fell face first into a planting of junipers, got a large dose of pollen and died. The boy's family successfully sued the city.