We have a tough dry spot in the garden (USDA zone 4) about 2' x 5' where a goldenrod cultivar would go nicely. The native species, although attractive, has a tendency to seed freely and be almost impossible to remove.
Are the cultivars more manageable, or do they seed freely and propagate by rhizomatous roots like the native species?
It really depends on the exact variety you choose, some are "clump forming", while others are more like the native species you mentioned -- will naturalise.
Varieties that naturalise can be controlled (somewhat) by dividing the plant every 2 or 3 years.
Some "clump forming" varieties:
Some "will naturalise" varieties:
All of the above plants are approved for UDSA hardiness zone 4.
