Shrubs are generally characterized by rather limited flowering periods, so it is a good idea to choose them based on the posture and shape and color of the leaves, rather than for their flowering.
An exception is the Hibiscus syriacus, a shrub native to the Eastern world that combines great rusticity with the ability to produce abundant flowers throughout the summer.
Precisely because of this characteristic, many varieties have been selected over time with magnificent inflorescences, with colors ranging from the purest white to pink and red, up to shades of purple and blue.