If your allergies act up in late summer, don’t blame goldenrod. “What’s making you sneeze is ragweed,” said Sharon Yiesla, plant knowledge specialist at The Morton Arboretum in Lisle.
Goldenrod is easy to accuse because it seems to be everywhere between August and November, with feathery wisps of yellow bloom in gardens, in prairies, and along roadsides. Yet the real culprit is ragweed, which blooms at the same time.
The difference is in the plants’ pollen, which is essential for their reproduction. Ragweed is wind-pollinated, so it produces many minuscule grains of pollen, each light enough to be wafted by a breeze to pollinate a female flower — or land on a human and cause an allergic reaction. A single plant can produce millions of these tiny pollen grains.
Goldenrod, on the other hand, is pollinated by insects that fly from bloom to bloom. Its pollen grains are large, heavy and sticky, because they have evolved to hitchhike on an insect’s legs. They can’t fly away to trouble your nose.
Ragweed is a serious problem for people. Up to a fifth of all Americans suffer from allergies when ragweed is in bloom and it is a leading cause of asthma attacks.
Two ragweed species — with the ironic scientific name of Ambrosia — are listed as noxious weeds in Illinois. Both have hairy stems and the deeply indented leaves that give these plants their common name. Common ragweed (Ambrosia artemisiifolia) grows about 2 to 3 feet tall. Giant ragweed (Ambrosia trifida) is usually 6 to 7 feet high but can reach 10 to 12 feet in ideal conditions. Although they have unfortunate effects on humans, these ragweeds are native plants, with a role in Midwestern ecosystems.
Both plants produce small brown seeds that are attractive to birds, which spread them far and wide. The plants can sprout in a wide range of conditions and the seeds can persist in the soil for years.
“Ragweed is pretty much inescapable, because the plants can grow in so many places, they produce so much pollen and the pollen grains float so far,” Yiesla said. The changing climate has caused the ragweed allergy season to grow longer by more than two weeks since 1995, according to the U.S. EPA.
You can at least make a dent by pulling ragweed plants from your own yard before they begin to bloom in June. The small flowers are green and inconspicuous.
“Just don’t remove goldenrod,” Yiesla said. “It’s very valuable for wildlife, especially since it blooms in late summer and fall when many other plants are done flowering.”
More than a dozen species of goldenrod are native to Illinois. There are goldenrods adapted to every kind of habitat — prairie, savanna, woodland and wetland. You can enjoy the yellow blooms of a number of different goldenrod species in the Arboretum’s gardens and natural areas in late summer and fall.
A wide variety of insects visit the flowers for pollen or nectar, including bees, butterflies, moths, wasps and beetles. Caterpillars of many insect species feed on the foliage, and the seeds are attractive to goldfinches and other birds.
“Goldenrods can be wonderful garden plants,” Yiesla said. Canada goldenrod (Solidago canadensis), the most common species in the Midwest, may not work in every space because it can get up to 6 feet tall. “If you’re looking for a smaller plant, there are other possibilities,” she said. “Because goldenrods grow in so many different habitats, there are species that
can handle varying soil and light conditions.”
Consider stiff goldenrod (Solidago rigida); elm-leafed goldenrod (Solidago missourienis); early goldenrod (Solidago juncea); Ohio goldenrod (Solidago ohioensis); showy goldenrod (Solidago speciosa); rough goldenrod (Solidago rugosa); or zigzag goldenrod (Solidago flexicaulis). A few commercially cultivated varieties, such as Fireworks goldenrod (Solidago rugosa ‘Fireworks’), have been selected for garden use.
As a garden plant, goldenrod’s most common problem is powdery mildew. Some species such as Canada goldenrod also spread vigorously through underground runners.
“Goldenrod is such a powerful wildlife plant and such a pretty sight in late summer that it’s worth considering for any garden,” Yiesla said. “And it won’t make you sneeze.”
For tree and plant advice, contact the Plant Clinic at The Morton Arboretum (630-719-2424, mortonarb.org/plant-clinic, or plantclinic@mortonarb.org). Beth Botts is a staff writer at the Arboretum.
