Sunday, September 4, 2011

Ragweed, not Goldenrod, is the culprit!

When the season of Goldenrod begins - the clusters of tiny yellow flowers gradually appearing on roadsides, I am careful to point the plant out to people.  The reason I do this is because I know that a lot of people think that Goldenrod (Solidago spp.) is the cause of fall allergies.  They often exclaim “Oh, that stuff bothers my allergies!”  That is my cue to educate them about the true culprit: Ragweed.

Goldenrod, likely Solidago altissima

Ragweed (Ambrosia spp.) quietly appears on roadsides around the same time.  The most familiar one around here is an annual plant: Ambrosia artemisiifolia.  The foliage is deeply cut – many gardeners mistake it for a seedling of Cosmos sulphureus, the familiar orange garden Cosmos.  People who aren’t gardeners just overlook it.  Another member of the same family is giant ragweed, Ambrosia trifida.  Even though it is also an annual, it grows to be over 10 feet tall in one season!  

Ambrosia artemisiifolia

While Goldenrod has bright yellow flowers, Ragweed flowers are green. The color of the flowers allows Ragweed to continue to be overlooked and ignored – people don’t even realize it is blooming.  When the allergens take to the wind, and people look for something to blame, it is the Goldenrod flowers that they see.

Could it be that both flowers bother you?  After all, if they are both blooming then they must both be throwing their pollen around, right?  Actually, the ability of pollen to fly through the air is limited by its own weight.

Plants that cause allergies have very light, dry pollen, and those plants rely on the wind to carry their pollen to another plant (of the same kind).  Plants with lightweight pollen include: oaks, hickories, mulberries and pines (spring), grasses (summer and fall), and ragweed (late summer to fall).  In fact these plants have non-showy flowers without petals that are just made for wind-pollination.

Ragweed flowers open and releasing pollen

In the picture above you can see the flowers. They don't have any petals - this is all they will ever do in terms of blooming. They don't need petals to attract any insects as the wind facilitates their pollination; in fact, petals would only get in the way!  As I was taking this picture, numerous grains of pollen were released from the flowers each time that I moved the plant.

Plants that are insect-pollinated have heavy, sticky pollen that is not picked up by the wind.  These plants have showy flowers that attract pollinators like bees, wasps, butterflies and birds.  The pollen brushes onto the pollinator and is then carried to the next plant that the critter visits.  Goldenrod is just such a plant.

Goldenrod flowers (Solidago altissima)

So now you have a perfectly logical reason to help you remember that Goldenrod is not a bad guy.  As the roadsides light up with the showy, yellow flowers of our native Goldenrods this season, you can smile and enjoy the show instead of eyeing them with dread.


  1. Great post, Ellen! I love seeing other blogs educating people about native plants. I blog about pollinators, so I was excited to see you talk about them a little too. I just wanted to add that goldenrod is a really important pollen and nectar source for lots of pollinators because it tends to grow (and bloom) in large masses, and for several weeks. :)

  2. Ellen,
    So glad you did this post. Such a common mix up with our beloved Goldenrods. The same goes with Yellow Jackets (not bees) being a nuisance at picnics.

  3. Thank you Ellen! Goldenrods are some of my favorite and the misconception goes on. That's what they get for being so much showier than the ragweed culprits. I did a piece a while back that included some details on allergens in the garden over at Glad you are getting the word out!

  4. Yes, thank you Ellen. This misconception is a real pet peeve of mine. Just last year, I spotted a banner in a grocery store (with a pharmacy) that had a picture of a snipped goldenrod flower head with the title "Allergies?". It *really* bothered me that this ad was reinforcing this false perception.

    Thanks for helping to educate people.

  5. This time of year it is popular to state that "it's the ragweed, not the goldenrod." But I've never seen anyone go into the details of why ragweed can be irritating to us, as other plants & trees are. Thank you, Ellen.