How to - The Healthy Gardener

Combatting allergies in the garden

Keep those pollen-producing plants out of the garden

If you love gardening but hate the allergies you suffer through, changing what you grow could help. Pollen-producing plants are the main culprits in allergy attacks; identifying plants that are the largest producers of pollen and keeping them out of your garden could help keep allergy symptoms at bay. While other substances such as mould can trigger allergy attacks, American horticulturist Thomas Ogren believes that the widespread use of pollen-producing plants may be contributing to the growing number of allergy sufferers.

In the past 20 years, allergy rates have doubled in North America, and about 20 to 25 per cent of Canadians suffer from hay fever. Identifying the worst offenders is the first step in limiting exposure. Ogren has developed a plant allergy scale that rates plants on their allergy-causing potential. British horticulturist Lucy Huntington has designed low-allergen show gardens in the U.K. and U.S. Both horticulturists were motivated by having family members who suffer from allergies.

Dr. Gordon Sussman, a staff physician and allergist at the Wellesley Hospital in Toronto, doesn't believe that allergen exposure can be completely eliminated. While people may control what goes into their gardens, they're still exposed to pollens from elsewhere, he says. But Ogren believes the benefits could have an impact on a larger scale if there were more widespread use of allergy-free plants in landscaping.

When selecting plants, it helps to know how they pollinate; this can tell you how much pollen the plant produces. Some plants have pollen producers (male) and pollen receivers (female) together in one flower, which is called a perfect flower. An example is a rose.

Pollen only moves within the flower--it doesn't need to travel through the air to reach its target--so such plants are low pollen producers. Monoecious plants have separate male and female flowers, but they are on the same plant. Corn is one example: the tassel is the male flower and the kernels are the female flowers. Pollen is airborne while it travels to the female flowers, where allergy sufferers can breathe it in.

Dioecious plants also put pollen in the atmosphere; all the flowers are either male or female, and pollen has to travel between plants. For example, many junipers are separate-sexed. One key strategy is to select female plants--not easy to do as the sex of a plant is rarely listed alongside growing recommendations.

Ogren says that allergy-provoking culprits are often male plants, which are widely used because they don't litter the ground with seeds or pods. "I'm keen on pushing female plants because they actually remove pollen from the air," he says. There are no simple, visual clues as to the sex of a plant, though non-berry producing plants are often male and some cultivars are entirely male, such as Ginkgo biloba 'Autumn Gold', which is propagated by cuttings. Plants that have small, light pollen, such as oak trees, should be avoided as the pollen is easily blown about and inhaled into lungs, says U.K. horticulturist Huntington. Many grasses also fall into this category. She advises against daisy-like flowers, while most of the big flowers, such as peonies, are okay because their pollen is heavy and sticks to the plant rather than becoming airborne.

If you can't get rid of all your high-allergen plants, keep them away from windows or patios and keep them at the back of beds and borders. For many high-allergen trees and shrubs, pruning hard once a year results in few or no blooms, and therefore less pollen, says Ogren.

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