Dr. Leonard Perry, Extension Professor
University of Vermont
Generally pollen from plants, but also mold, dust, and even scents, can cause allergic reactions in some people. If you’re one of these, you don’t have to give up gardening during part of the season, or have to convert your landscape into silk flowers, gravel beds, and garden gnomes or plastic flamingos! Changing some gardening practices, or choice of plants, may be all that’s needed to lessen the symptoms.
According to WebMD.com, allergies can have some significant impacts on society. Ragweed pollen has increased in the last 10 to 15 years by four weeks, likely a result of global warming. As a result of hay fever, it’s estimated that 4 million workdays are lost each year. While one in five Americans have symptoms of allergies or asthma, 55 percent test positive to one or more allergens. Allergies, by one estimate, cost the health care system and businesses $7.9 billion per year. Some asthma in children is induced by allergies.
Most people see the yellow pollen on their car in spring or summer and think that’s what is causing allergies. But this relatively big, showy pollen such as from white pines isn’t really the culprit, but perhaps microscopic pollen that you don’t see, coming from other plants. Mowing lawns can stir up allergenic particles which may have settled and accumulated. So, if you find allergies more pronounced while mowing or nearby, a dust mask may help.
Pollen from plants is the main culprit in gardening allergies, and the one we can do most about. Avoiding exposure to pollen, either from not planting certain plants, keeping a distance from those plants that produce irritating pollen, or using proper culture, are the best means to minimize allergy symptoms.
Keeping pollen-producing trees pruned, and allergenic shrubs sheared, both reduce pollen and allergies. Many don’t realize that the common boxwood shrub has flowers, and that these produce pollen that’s allergenic to some people. It blooms on second year-old wood, so keeping these pruned yearly keeps the inconspicuous flowers from forming. Other culture such as proper placement of plants, watering, fertilizer, and pest control will reduce insects and diseases. Some may be allergic to insects, as well as to disease spores.
Author Thomas Ogren, in his book Allergy-Free Gardening, uses the phrase “proximity pollinosis”, which simply means that the closer you are to a plant producing allergenic pollen, the greater your exposure and better chance of symptoms. So not planting such plants near schools and schoolyards, patios, in public spaces, or under home windows that you open are all means to reducing allergenic pollen exposure.
So what plants are best? As with most such questions, the answer is that it depends. Allergies, of course, vary with each person as well as with plants. Some plants with showy, large flowers may have larger pollen that doesn’t blow around and cause problems, yet others do (such as the catalpa, with large flowers but small pollen). Some plants may remain in a young or juvenile state, and never bloom.
If trees have separate sexes, such as ash, willows, poplars, and some maples, the female plants won’t produce any pollen. Males of the hornbeam, silver, or box elder maples, junipers, and ginkgo are bad for pollen while their female plants are fine. (Yet the female ginkgo produces rather foul-smelling fruit so is seldom found.)
One cultivar (cultivated variety) of a plant may produce allergenic pollen, yet another may be sterile or produce no allergenic pollen. “Seedless” trees may not litter the ground, but they may be males that shed pollen as with some cultivars of White Ash. For red maples, ‘October Glory’ or ‘Autumn Glory’ are among the best for pollen, while you should avoid ‘Autumn Spire’, for instance. ‘Autumn Fantasy’ and ‘Indian Summer’ are a couple of good Freeman maples. Some sweet cherries (often the self-pollinating ones) may cause few problems, yet other cultivars may be highly allergenic to some people.
Ogren has developed the Ogren Plant Allergy Scale (OPALS) which you can learn about in his book or website (www.allergyfree-gardening.com). It rates plants from 1 (low) to 10 (high) for pollen and allergies and is useful in determining what plants to buy if allergies are a concern, with an extensive plant listing in the book. The scale incorporates many factors, such as the pollen traits, and whether a plant causes allergies from odor or contact as well.
Often, related plants may cause allergies. Perhaps 30 percent of those allergic to ragweed will also be allergic to the related goldenrod. Some daisy-type flowers in the composite family cause allergies, such as asters or chrysanthemums for some people. Flowers that are closed, and that bees or insects have to enter to pollinate such as snapdragons, generally don’t have pollen that blows about to cause allergies. While one to a few mildly allergenic plants may not cause problems, an abundance of them may cause hypersensitivity in some people.
You can learn more about allergies and their causes from websites of the American Lung Association (www.lung.org ) or the American Academy of Allergy, Asthma and Immunology (www.aaaai.org). Sites online can be useful to track pollen counts and air quality (such as pollen.com or airnow.gov).
Dr. Leonard Perry, Extension Professor