Some regard goldenrods (Solidago spp.) as mundane roadside and meadow weeds, while others see them as rustic wildflowers that bring golden-yellow color to late-summer landscapes. Members of the plant family Asteraceae, goldenrods number about 100 species found native in prairies, riverbanks or roadsides in North America and Eurasia. Goldenrods' precise blooming times depend on the species and your garden's location, but hybrid cultivars tend to flower more profusely and enjoy longer-lasting flower displays.
Flowering Time Frame
Among scores of goldenrod species and dozens of cultivars, general flowering time occurs between midsummer and midfall in the United States. August and September present the peak of goldenrod flowering in most locations. It's not unusual for some types to bloom beginning in mid-to-late July or continue flowering well into October. Late-blooming goldenrods continue flowering until the first fall frost puts an end to their blooms.
Goldenrod varieties may be hardy in from U.S. Department of Agriculture plant hardiness zones 3 through 9. In the northern U.S., the first fall frost comes early and cuts their flowering display short. By contrast, in the central and southern states, the same goldenrods continue blooming throughout fall, never harmed by frosts until flowering ends. Long, hot, southern summers trigger some goldenrods to bloom in August, while the same species father north flowers the following month.
Flowering periods vary significantly between goldenrod species and cultivars, with cultivars often blooming earlier and longer. These cultivars were bred and selected specifically for their prolific flowers and extended flowering period. Many gardeners consider goldenrods the most reliable late-summer and early fall perennial blooms. When early summer blooms have stopped, but early fall perennials aren't yet flowering, goldenrods carry the show. Local botanical gardens and extension offices can provide insight into precise timing for goldenrod blooms in your region.
Goldenrods and Pollen
For many years, goldenrods' golden-yellow blooms carried undeserved blame for causing hayfever. But the large, coarse pollen grains in goldenrod blossoms do not become airborne. Annual ragweeds (Ambrosia spp.) are the true culprits behind late-summer allergies. Tiny ragweed flowers occur the same time as various goldenrod species, but they attract much less attention. People wrongly assume the conspicuous goldenrod flowers are behind their hayfever, when ragweed is at fault.