Purple Coneflower vs. Black-Eyed Susan for My Garden

Descriptions

• Purple coneflower is a herbaceous perennial plant that grows 1 to 5 feet tall and up to 3 feet wide. Its strong, hairy stems bear daisylike flowers in shades of pink or purple with dark-purple centers.

  Black-eyed susan is typically an annual plant but may be biennial or perennial in warm climates. It grows 1 to 3 feet tall and 1 1/2 to 3 feet wide. Its red, orange or yellow, daisylike flowers have dark-brown or maroon centers.

Culture

• Purple coneflower is hardy in U.S. Department of Agriculture plant hardiness zones 4 through 10 or zones 3 through 9, depending on the source. Black-eyed susan grow in zones 2 through 11. Both kinds of plants reseed prolifically, and some gardeners consider them aggressive plants that take over flowerbeds.

  Both plants grow best in moist, well-drained soil that contains organic matter, although they will grow in most kinds of soil. Purple coneflower tolerates wet soil sometimes. Both plants grow in partial shade to sunny locations but benefit from some shade in hot climates. They are drought-tolerant, but purple coneflower does not grow as well in dry areas with full-sun exposure. Black-eyed susan's soil salt tolerance is considered good while purple coneflower's is considered poor.

Diseases

• Black-eyed Susan is prone to more diseases than purple coneflower. Verticillium wilt is a deadly disease that affects black-eyed Susan. Downy mildew causes mottled yellow leaves, and white smut results in light-colored spots on the leaves of black-eyed Susan. Gray mold produces fuzzy, gray, fungal growth on purple coneflower. Both species are affected by bacterial leaf spots and powdery mildew.

Pests

• In northern gardens, Japanese beetles chew on the leaves of purple coneflower. In all areas, leaf miners and sweet potato whiteflies damage purple coneflower's foliage while vine weevils damage its roots.

  Four-lined plant bugs cause brown, rounded, sunken spots on the leaves of black-eyed Susan. The spots often are mistaken for damage caused by a disease. Aphids suck sap black-eyed Susan foliage, and goldenglow sawfly larvae eat the plant's leaves.