Perennial sunflowers Helianthus spp. are long-lived cousins to the giant annual sunflowers H. annuus often grown in vegetable gardens. Perennial sunflowers are also more refined, with finer foliage and smaller flowers, but some types still grow up very tall. They're good plants for attracting birds and butterflies into the garden, and the flowers last a long time when cut. Most perennial sunflowers require full sun and well-drained soil for best growth.
One of the tallest perennial sunflowers available to home gardeners is Maximilian's sunflower Helianthus maximiliani. This native wild flower grows 6 to 7 feet tall, although it can grow taller or shorter depending on soil conditions and available moisture. The narrow plants have 3-inch, bright-yellow flowers all along the top third of the stems in mid to late summer.
Flore-pleno H. multiflorus "Flore-pleno" is a hybrid sunflower bred specifically for home gardens. It grows 4 to 5 feet tall with a similar width and is covered in double, golden-yellow flowers all summer. Hummingbirds, other birds and butterflies are all attracted to the showy flowers. Unlike many sunflowers, Flore-pleno flowers well in partial shade. It's pest and disease free and is hardy in U.S. Department of Agriculture Plant Hardiness Zones 4 through 10.
Adaptable to different light and soil conditions, the thin-leafed sunflower H. decapetalus grows up to 5 feet tall in full sun or partial shade. The abundant flowers are bright yellow with a greenish central cone and are long lasting as cut flowers. When deadheaded, the plant puts out side branches with even more flowers. Thin-leaf sunflower is at its peak in late summer and early fall.
Native to the East Coast, the swamp sunflower H. angustifolius has yellow flowers with dark centres. As the name implies, it tolerates moist soil, an unusual trait among sunflowers. It comes into bloom late in the season from late August until October. Swamp sunflower grows 5 to 7 feet tall.
Native to the East Coast, the woodland sunflower H. divaricatus is another good choice for shady locations. As the name suggests, it grows naturally in wooded areas. Woodland sunflowers grow 3 to 5 feet tall and have solitary, clear-yellow flowers with long, tapering petals in midsummer. The leaves are very stiff and textured like sandpaper. It's a good sunflower for naturalised gardens that are partially shaded.