What Makes Common ragweed Weedy

•  It gives people hay fever.

•  Proliferates quickly in disturbed soil by virtue of enormous seed production and adaptable (see Q#7) reproductive systems. Its swift germination, and rapid development help it dominate newly exposed areas as a first generation annual invader.

•  Shallow roots enable it to find air in many kinds of soil including difficult, compacted, disturbed, barren soils where little else can grow.

•  It adapts to tough conditions where it thrives on lower competition, thwarts most efforts to poison it, and it changes form rapidly, eluding control.

•  Since it flowers in the fall, it easily hides its early growth, when its foliage most resembles other plants, amidst the more abundant flora of summer.

As Ragweed pollen drifts, its tiny particles dismay allergy sufferers. Only clouds of tiny and jagged wind-born pollen such as that produced by the inconspicuous florets of Ragweed (and many wind-pollinated Grasses, Trees and other plants) can produce hay fever. Not until 1873 did Charles Blackley find the causal agent of hay fever. People still believe, albeit incorrectly, that Goldenrod, Solidago, which blooms at the same time, and which coincidentally has the same jagged pollen, causes hay fever. But Goldenrod’s pollen weighs too much to float prolifically. Further, Goldenrod’s pollen cells are too large to cross the barrier of most mucous membranes. Goldenrod relies on bees, not breeze, for pollination.

Above: Electron micrograph of Ragweed pollen, Photo Credit: CDC / Janice Haney Carr

The photo clarifies just how spiky its pollen is. It helps explain how its tiny pollen grains can gain a grasp on the surface of mucus membranes.

On the plus side, it offers food and shelter to birds and other wildlife. Common ragweed has increased in number as people break more ground to make way for buildings, farms, and gardens. Once ground breaking stops, it balances out in a native ecology, allows for plant diversity, and opens up and improves previously barren, eroded or compacted soil.

Red sorrel, Rumex acetosella is another weed I came to recognize in my garden, after I spotted it in other compacted, acidic and impoverished soil sites. It flourished in a distressed spot that I occasionally drove over, accidentally—the corner where the driveway and roadside met and surrounded a small patch of ground I had tried to plant with flowers. Wedged between two hardscapes which were subject to road salting, Sorrel killed off anything that tried to grow in its sturdy, unfriendly path. Before you ruminate too long, “ex” out this acidic tasting thin red invader or you’ll be perennially sorrel, I mean sorry. Folklore aptly dubs Red sorrel “a child of calamity” and proclaims that “Sorrel stores strife”.

Unlike Common ragweed, this is a tough non-native perennial. It rates “noxious weed” status in 23 states.

Its deep perennial taproot grows down as much as 5’ plus it forms an extensive side root network up to 10-30’ long. Even in very young plants, below ground root growth far exceeds its above ground shoot growth. Taproots in turn grow root buds that grow clones, up to 3,500 shoots in 2 seasons of growth alone, so identical colonies last for decades, though individual plants last only 18 months. Roots emit “allelopaths”, chemicals toxic to other plants. Since it performs poorly as an erosion control and keeps the soil anaerobic and full of keep-out chemicals, it remains dominant and harms nearby plants.

Left: Red sorrel taking over a patch of poor, compacted, clay soil Right: Roots exceed shoots on this baby Sorrel.

Like Common ragweed the male florets of Red sorrel spread tiny, light weight pollen. Its pollen is similar in shape to the type spread by Common ragweed. As tiny Red sorrel pollen floats in the wind it, too, activates allergies in the pollen-sensitive. The multitude of the seeds it spreads magnifies the power of its roots. Red sorrel produces as many as 450,000 seeds per plant that last up to 20 years in the soil seed bank, launches seeds into a whirlwind, and germinates plants in a mere 3 to 4 weeks. Ants help disperse mature seeds.

On the positive side, it feeds bees, butterflies, birds, and small mammals. To some, it tastes lemony and piquant and has a rich culinary and medicinal history. Though noted as a thirst quencher as early as the time of the Romans, I find it too sour to enjoy. Since it indicates poor conditions, it impugns my gardening abilities, so I personally find it undesirable. Plus it grows in such unappetizing conditions. Other less tasty uses include: cleaning wicker furniture, removing water spots from wood, ink from linen, rust stains from clothes and porcelains, making dyes especially for wools, and making paint.