Solidago are perfect for providing fresh blooms in the difficult late summer/early fall time slot and provide a great backdrop for mums and other late bloomers. It has gotten a hayfever reputation because it blooms at the same time as Ragweed - Goldenrod does not aggravate hayfever!
Avoid overly rich soils. For compact plants, cut back by 1/2 in June, or pinch back in May. This may delay bloom time. Can be divided every 2 - 3 years in spring. May need frequent division to maintain boundaries in formal border. Spent flower stalks provide winter interest, but can be cut down to prevent over seeding.