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, is the cause of allergies. 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 or 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 boxelder 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, such as asters or chrysanthemums, cause allergies 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).
Dividing groundcovers, edging garden beds and watering properly are gardening activities for this month.
Ground covers such as carpet bugle, perennial vinca, pachysandra, ivy, spreading foamflowers (some new cultivars form clumps instead), and deadnettle or lamium can be divided and transplanted now to create new beds, to enlarge existing ones and to replace turfgrass especially under trees where it grows poorly. On a cloudy, cool day, use a sharp shovel or trowel to separate offshoots from mother plants and transplant them into a shady new location. Keep them well watered. Some of these spread quickly in good soils, so site them carefully. A solid edge between beds and lawns may be needed if they get out of bounds.
If groundcovers start to spread out of bounds, or if you don’t have an edging material around the borders of your garden beds but want a trim appearance, use a flat spade to shave off clumps of sod to define the edges. You’ll probably need to do this a couple of times, but if you don’t you’ll be fighting encroaching grass all summer. There are hand and electric edger tools just for this purpose.
A frequent sprinkling from the hose is primarily beneficial for keeping seeds moist until germination. Most trees and shrubs need deeper watering both to encourage new roots to grow deeper and to reach those deep roots of established plants. Watering often and lightly will just encourage roots to stay in the top couple of inches of soil where they will be very susceptible to drying out. It’s best to set up a sprinkler for half an hour and then dig to see how deeply the water penetrated. If it didn’t reach the depth of the root ball, or at least 8 inches, set the sprinkler for another half hour and check again.
Grubs are short, squat white larvae that feed on roots of lawngrasses and other plants, and eventually turn into beetles that feed on leaves. While you’ll see recommendations and ads for products to apply now for these, the best biological controls are beneficial nematodes. These are best applied in late summer during the young stages of new grubs.
Milky spore is another organism that attacks grubs, but only those of the Japanese beetle. There are other types of grubs, such as those of the rose chafer and Asiatic garden beetle, so before using this product make sure you know which grubs are present. Your state Extension diagnostic lab can identify grubs (www.nepdn.org). Milky spore is often not recommended by insect professionals in New England as it is less effective and spreads more slowly in cold climates and soils, needs to be applied over a larger area than a home landscape to be very effective, takes 2 to 4 years to work, has variable results, and at best only will keep populations of grubs lower and not eliminated.
One recommendation you’ll often see and hear is to apply Epsom salt (magnesium sulfate, not related to table salt) to improve fruiting of tomatoes and peppers. The reality, if one examines the research on this chemical back to early in the last century, is that it does correct and has been effectively used for magnesium deficiency in soils or plants. Other than this, adding too much may affect availability of other nutrients, causing other deficiencies, and add to water pollution (www.informedgardener.com). In most gardens magnesium deficiency doesn’t exist.
Editor’s note: Leonard Perry is a professor with the University of Vermont Extension and Charlie Nardozzi is a nationally known horticulturist, author, gardening consultant and garden coach.