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If you are suffering from allergies, tree and plant pollen may be the reason.


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Your Earth: Friday, May 18th, 2001

*Note: This article first appeared in several Canadian newspapers and also in ENN.

Victoria Day marks the official start of the gardening season. This weekend, would-be gardeners will be lining up to buy all the plants and flowers they need to landscape their yards.

Not coincidentally, this is also the beginning of allergy season for millions of seasonal allergy sufferers. For these unfortunate souls, the warm weather means months of itchy watery eyes, runny noses and a longing for the first frost of fall.

The number of people who suffer from allergies is increasing every year. As recently as one hundred years ago, allergies were so uncommon that they didn't even have a name. By 1959, the Encyclopedia Britannica estimated that somewhere between 2 and 5 per cent of the population suffered from some kind of allergy. According to the American College of Allergy, Asthma and Immunology, by 1999 that figure had increased dramatically to 38 per cent. Childhood asthma is now the number one chronic disease suffered by our children.

This exponential increase in the incidence of allergies and asthma has been blamed on everything from smog and air pollution to reactions to the chemicals in our food and water. Landscape gardener, teacher and writer Thomas Ogren has another theory. He says that the severity of seasonal allergies is directly related to an increasing trend toward using male trees and scrubs in landscaping.

"These male clones are also sometimes called "litter-free" trees and shrubs since they do not drop any seeds, seed-pods, or fruit on the lawns and sidewalks," said Ogren. The problem with separate-sexed male plants in the landscape is that they all produce large amounts of allergenic pollen. And according to Ogren, the vast majority of trees we plant are males.

Ogren explains that this situation is being made worse by the lack of biodiversity in the urban landscape. He says that typical landscapers feel comfortable with about a dozen different varieties of plants suited to a particular climate or region. As a result, we are being overexposed to the same type of plant pollen. Overexposure to anything can create a sensitivity that ultimately leads to allergy.

Dr. David Stadtner is a retired allergist who says that Mr. Ogren is 100% correct. "With the increase in affluence, people are spending more money on landscaping, and they are also spending more time in their gardens," he said. "Unfortunately, people are planting the wrong things." While Dr. Stadtner admits that we don't know why people get allergies, we do know what triggers them, and pollen is a major culprit.

The solution, according to Ogren, is allergy-free landscaping. Planting a wide variety of pollen-free or low pollen producers is not only healthier for humans, but it also creates a more diverse, resilient landscape. Following Ogren's prescription for an allergy-free garden not only makes common sense, but it also creates a much healthier garden. For example, female sod lawns are actually easier to maintain and require less frequent mowing than male lawns. Female plants -- especially trees -- are natural air-cleaners. According to Ogren this is because the flowers on female trees are positively charged and airborne pollen is negatively charged. This makes the two mutually attractive, and removes allergy-causing pollen out of the air.

Critics of Ogren's theory say that pollen knows no boundaries and can blow in from just about anywhere. And while Ogren concedes that some pollen does blow in from far way, the majority of the pollen falls close to where it originates. "This means that an allergenic pollen-producing tree in your own yard, will expose you to 10 times or more pollen than would a similar tree planted just down the block," said he. "Gravity affects everything -- including pollen. With trees, the largest amount of pollen usually lands under the tree itself, or very close to the tree's drip-line."

According to Ogren, allergy is often very localized. For example, frequently cases of allergy are seen where people have male shrubs of species such as Yew or Juniper planted right under bedroom windows. Pollen is tiny and can easily pass right through the tightest window screens.

For more information about Tom Ogren's theory, read his book, "Allergy-Free Gardening" (Ten Speed Press, 2000).

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