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by Janet Davis
by Janet Davis


Janet Davis is a freelance garden writer and horticultural photographer whose stories and images have been featured in numerous publications. Magazines featuring her work include Canadian Gardening, Canadian Living, Gardening Life, President’s Choice Magazine, Chatelaine Gardens and, in the United States, Fine Gardening and Country Living Gardener.


September 16, 2001

jdRagweed.jpg (38137 bytes)Aaah-choo!

It’s ragweed time again, when millions of North Americans sneeze and wheeze and cough their way through summer’s last hurrah, miserably praying for relief. Alas, relief from this year’s pollen invasion won’t be felt until millions of pesky ragweed plants are laid low by frost.
For many years, when friends or relatives complained about their ragweed allergy, I tried to commiserate, offering a lame “Oh well, it’ll be over soon” and going my dry-eyed way, thankful for my pollen-repelling genes. Until one hot, breezy night a few Augusts ago, that is, when I awoke mid-sneeze at 2 a.m. with my nose twitching, my eyes itching and a little voice somewhere cackling “Gotcha, smarty-pants!”

Ragweed is an annual whose botanical name Ambrosia qualifies as one of nature’s sick jokes. Common ragweed or Ambrosia artemesifolia grows from 6 to 60 inches tall and, as the name suggests, has lacy artemesia-like leaves. It might be the most common weed found on sunny land in much of North America, popping up in neglected gardens, roadsides and disturbed fields. Numerous, tiny nondescript greenish flowers cluster in stalks on the upper branches, blooming for a long period from August through October until frost. (It’s a characteristic of wind-pollinated plants not to waste too much creative energy on the pretty, fragrant, colourful flowers that insect-pollinated plants produce to attract their pollinators.)

Giant ragweed or Ambrosia trifida can reach 9 feet in height and is a little fussier about where it grows, preferring rich, moist soil near streams -- like the ravine park down the street from my house, where naturalization and reduced park budgets have allowed it to colonize its merry way along the creek at the bottom of the hillside. Giant ragweed has large, pointed, three-lobed leaves and strong, fibrous stems which native Americans used to make rope.

Although ragweed bears flowers of both sexes, it’s the males (ahem) that cause all the aggravation, with a single plant capable of releasing billions of pollen grains into the air nightly in the hopes that some will fall on the female seed-producing flowers which are tucked into the leaf axils below. While this scattergun approach effectively guarantees next season’s population explosion, the toxic nature of ragweed pollen and the fact that it can float more than a hundred miles on the wind make it virtually impossible to control. In fact, someone (a pollen volume actuary?) offered the estimate in a drugstore publication on allergies that “well over 300 million tons” of ragweed pollen are launched over the central and eastern areas of the U.S. and Canada during August and September. Because ragweed is shallow-rooted, however, it’s easy to pull out in spring before flowers appear—a good way to control it locally.

So how do windborne allergens work? When a pollen grain or a bit of cat dander or a yucky little house dust mite (yes, even YOUR matress cover is littered with these microscopic dead skin eaters) is inhaled by a susceptible person, the immune system rises to do battle. Mast cells begin making chemical reactants including histamine, to neutralize the allergen. Excessive histamine causes rhinitis — runny nose, itching, sneezing, etc. Anti-histamine drugs like Reactine and Claritin block the manufacture of histamine.
While ragweed pollen is the most prolific and toxic windborne pollen allergen, it’s by no means the only one. In May and June, pollen from flowering Kentucky bluegrass (in uncut lawns), timothy grass, and the nondescript flowers of maple, birch, poplar, beech and oak can cause allergic reactions. Goldenrod, often tagged as the allergen culprit because it blooms simultaneously with ragweed, depends primarily on a host of insects rather than wind for pollination, so its sticky pollen is not carried in the air (although studies indicate it can cause allergic reactions in some people).

This year, I’m feeling a big smug about “sneezin’ season”. In this hottest of Ontario summers, a new air conditioner has finally given me blessed relief from the clouds of ragweed pollen that used to waft in through the open bedroom windows for 6 weeks or so from August ‘til October. In fact, it’s only when we linger after dinner to finish our wine in the garden that I feel my eyes begin to itch and my nostrils twitch and before you know it….


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