Why do zinnias grow back?

Zinnias are annual plants, meaning they typically complete their life cycle in one growing season. However, they can sometimes appear to "grow back" due to self-seeding, where seeds from the spent flowers drop to the ground and germinate in the following season. Additionally, zinnias are often cut back or deadheaded, which can encourage new growth and prolong blooming. In favorable conditions, this can create the impression of regrowth.