Believe sunflowers and you probably conjure up images of taller-than-life plants using larger-than-life yellow flowers that reach toward the sun. Perennial sunflowers, like Maximilian (Helianthus maximilianus), grow from underground root constructions called rhizomes and typically, they don’t grow quite as tall and big as their annual pals. Hardy in U.S. Department of Agriculture plant hardiness zones 4 through 9, perennial sunflowers benefit from pruning to control their stature and also to help them grow thick and lush with a great deal of flowers.
Cut taller kinds of perennial sunflower back from one-half, in late spring or early summer, then by another one-third a month afterwards. You can cut fall-blooming varieties a third time if necessary until late summer, but once the buds form, halt pruning. This helps control height since staking them may be hard.
Pinch or cut off spent flowers when they begin to fade to support perennial sunflowers to produce more blossoms. Do this during the flowering season till the last wave of flowers, typically in late summer or fall.
Cut back perennial sunflower plants into the ground in autumn after they are finished blooming and the foliage begins to fade. Do this to clean up your garden, if wanted. Should you wait until late winter or early spring to cut them back, then the seeds will provide food for the birds through the cooler months.