Goldenrod or Ragweed: Which One Causes Fall Allergies?

Gardening in the fall is lovely. The temps are cooler, the sky is a searing bright blue, and the maples and oaks are announcing the season with their brilliant display of red, orange, and yellow leaves. But your bliss is shattered when your eyes and nose start to run like a firehose, and sneezing comes on in fits. Inside you go with the doors and windows hermetically sealed.

Many blame the bright yellow flowers of goldenrod for their fall allergies, but the plant is wrongfully accused. The guilty party is goldenrod’s cousin ragweed, and the reason is how each plant is pollinated.

Goldenrod pollen isn’t carried in the air

Ragweed and goldenrod belong to the same family of plants, Asteraceae. Both plants bloom at the same time each year, from August through October, as do many plants in the Asteraceae family, which number over 100.

Goldenrod’s bright yellow flowers have large pollen grains that are too heavy and sticky to be carried on the wind. The plant relies on insects and birds to do the pollinating. When a pollinator lands on a goldenrod flower, the sticky pollen attaches to its body. As it moves between flowers, the pollen rubs off, pollinating the flower. That’s why goldenrod has such bright yellow flowers – to attract pollinators who feed on the nectar. The wind doesn’t play a role in goldenrod pollination, and the pollen doesn’t drift far from the plant.

Ragweed pollen is windborne

On the other hand, ragweed has very light, tiny grains of pollen, making it perfect for windborne pollination. Ragweed doesn’t have showy flowers like goldenrod to attract insects because it doesn’t need them – even a light breeze can do the work of pollinating ragweed.

Each ragweed plant can produce up to one billion pollen grains, each of which is usually carried on morning breezes until it lands on another ragweed plant, fertilizing the flower seeds. It might also land in your hair, on your skin, or in your sinus passages, causing an allergic reaction. As morning temps drop below 50 F, or if it rains, pollen production declines.

Goldenrod flowers contain nectar to attract pollinating insects, and the large, heavy pollen grains attach to the insect bodies. It is an important nectar source for pollinators. Ragweed flowers do not contain nectar, and the plants are dependent on the wind to transfer the small, lightweight pollen. This pollen has the ability to blow for miles. A single ragweed plant is capable of producing over a billion pollen grains.

Clemson Cooperative Extension

So why do you sneeze when working with goldenrod?

Ragweed pollen can travel far. It has been found in the air 400 miles out to sea and two miles up in the atmosphere. But most falls close to its source.

Asthma and Allergy Foundation of America

Most seasonal pollen allergies are caused by plants that rely on wind to move their pollen from flower to flower, so goldenrod cannot be the culprit behind those sneezing fits. But of course, sticking your nose in goldenrod and giving it a good sniff can aggravate your allergies as you’ll move that pollen from the flower to your sinuses. Or you might inhale ragweed pollen from the goldenrod, as the two plants frequently grow in the same areas.

How to tell the difference between goldenrod and ragweed

The differences between goldenrod and ragweed are pretty obvious:

• Goldenrod has bright yellow flower spikes that start to branch at the top of the stems. Its leaves are smooth. Goldenrods are perennials.
• Ragweed has unremarkable green flower spikes and many branches. Depending on the variety, its leaves may be dissected, similar to marigolds, or have a fern-like appearance. Ragweed is an annual and reseeds each year.
• Either plant can be found growing along roadsides or in forests in the Midwest and Eastern United States, and Canada. Ragweed will also appear in poor soil, vacant lots, pastures, meadows, along sidewalks, and in your backyard (ragweed runs rampant in mine – I pull it out all year).

So in effect, goldenrod gets a bad rap in the fall because it’s guilty by association: people sneeze, look around, and see bright yellow flowers – so they assume that’s what’s causing their allergies. But in fact, it’s the evil cousin ragweed. There’s one bad seed in every family, I suppose.

Goldenrods are considered “keystone plants,” species that have extreme importance to wildlife. Goldenrods support dozens of butterfly and moth species by serving as their caterpillar host plants. Goldenrods also support dozens of native bee species that are pollen-specialists and can only feed their young the pollen of certain native plants. Rapidly disappearing monarch butterflies rely on goldenrod nectar to fuel their long fall migration down to Mexico. Many native bee species nest and overwinter in the stems of… goldenrod, and many songbirds species feed on the seeds of goldenrod. So don’t cut back goldenrod seed heads or stems after the flowers stop blooming — leave them standing through winter.

National Wildlife Federation

Sources: Clemson Cooperative Extension, Asthma and Allergy Foundation of America, Tennessee Naturescapes, LSU Ag Center, Nature Conservancy Canada.