Ragweed Allergy: The Real Story Behind Allergy Season

It’s MOTHER EARTH NEWS FAIR time as I write this, and I am scheduled to speak about open-pollinated corn for backyard and small-scale growers. Whenever I get to tell tales of growing corn and keeping different varieties genetically isolated from one another, my mind turns to pollen and the ways it can travel to accomplish the task of fertilization. We all worry about the bees, and for good reason — they carry pollen from flower to flower in the process of doing what bees do. But that’s not how corn does it, and that’s why most people who think they are allergic to goldenrod are not having a histamine response to it, unless they rub it on their skin. Let me explain.

In general, most pollen is designed to either float on the breezes or be carried from place to place. The pollen that is wind dispersed readily sheds from the anthers on the flowers where it is born — take a look at a corn tassel some morning and give it a tap — at the slightest breeze. The wind then carries the pollen some distance, and in the more or less random event that it encounters a sticky stigma on a female flower (or flower part in the case of flowers with both male and female components) of the same species, successful fertilization may ensue. If it seems chancy, it most definitely is, which is part of the reason why plants with wind dispersed pollen make so much of that pollen. Corn is wind dispersed, but goldenrod is not.

It turns out that goldenrod is insect pollinated. Its pollen is heavy and sticky, and virtually impossible to blow off the flower. And if it was blown from the flower, it would not float on the breezes the way corn pollen does. No, goldenrod pollen is designed to stick to bees, flies, moths and other insects that visit the flower, and when they subsequently visit other flowers, they inadvertently transfer some of that pollen around, which may result in fertilization. But, what’s up with all the folks who suffer with wind-born allergies when the goldenrod is in full bloom?

Goldenrod has what botanists call a showy flower, which means it is highly visible and quite ornate — bright yellow on a late summer and fall landscape is tough to miss. So folks have a bad bout of hay fever and assume that goldenrod is the culprit. It is possible to be allergic to goldenrod pollen, but unless you ingest, inhale or otherwise expose yourself to it, you are unlikely to have any response just because the flowers are blooming. So, what gives?

Many plants have what botanists call non-showy flowers — by non-showy, I mean they tend to be green, often small and rarely noticed, much less chosen for bouquets. One such plant that blooms at about the exact time as goldenrod is ragweed. Common ragweed can readily produce a million pollen grains per plant per day, and it floats for hundreds of miles or more. Pollen shed for an individual plant might last for a couple of weeks — that’s a lot of pollen. Ragweed pollen is highly allergenic and is one of the most prevalent hay fever agents out there.

Lucky for me, corn pollen is not very allergenic, so I do not have any problem spending time in my corn patches, either hand-pollinating my special varieties or dreaming up new ways to keep all that airborne pollen in the right places. But that’s a topic for another day.