The three prominent and parallel veins on the underside of the leaf on the left are characteristic of Tall Goldenrod and Canada Goldenrod. The leaf on the left, with only a single prominent vein is Showy Goldenrod
Tall Goldenrod in the Garden
There are several of our native goldenrods that are very weedy and can aggressively invade gardens and other disturbed sites if not controlled. Tall Goldenrod (Solidago altissima) and Canada Goldenrod (Solidago canadensis) are very adaptable species that are able to grow in a wide variety of soil types and moisture levels.
In part they spread by wind-dispersed seeds, but the root system also produces long creeping rhizomes that can lead to the formation of dense colonies of plants. According to the Ohio State Weed Guide , the root system of Canada Goldenrod is very deep and fibrous with lateral rhizomes up to 5 inches long.
It is very difficult to differentiate between Tall and Canada Goldenrod. In fact S. altissima was, for a time, considered part of S. canadensis. However, the issue is not to correctly identify S. altissima vs. S. canadensis. Rather, it is more important to differentiate these two species from other taller goldenrods such as Stiff Goldenrod (Oligoneuron rigidum) and Showy Goldenrod (Solidago speciosa). The former is a flat-topped goldenrod, the latter has a very different venation pattern on the leaves.
A Minnesota web site, Friends of the Wildflower Garden, described Tall Goldenrod as “The plant can form dense colonies from its creeping rhizomes and of all the goldenrods, this one could be considered invasive as it spreads readily by the roots and by seed.” Because these species are long-lived and can create large stands to the exclusion of other species, it is important they be controlled. If you have these in your garden, they should be removed. It is easier to do this by hand pulling when the soil is moist and you have only a few in the garden. The Driftless Prairie offers a good discussion of other control options.