Rudbeckia triloba is an herbaceous biennial or short-lived perennial with many common names including branched coneflower, thin-leaved coneflower, three lobed coneflower and brown-eyed Susan. It is native to the prairies of the eastern and Midwestern US (New York to Florida, west to Minnesota, Utah and Texas), and is naturalized in open woods and old fields, and on rocky slopes in zones 3(5)-10.
The name “triloba” comes from the dark green, somewhat hairy basal leaves that are divided into three oval parts. This plant is similar to the very common black-eyed Susan (R. hirta), but is taller, flowers later and over a longer period of time and has much smaller flowers.
Masses of yellow daisies with brown centers make this a late-season garden standout. Plants burst into bloom in late summer through fall, or until a hard frost.
They produce abundant small (1-2″ across), flat, brilliant yellow flowers with button-shaped jet-black centers that fade to brown. The 8-10 ray flowers are proportionally shorter and wider than those of other coneflowers.
Flowers are produced at the ends of many-branched, erect stems with narrow leaves, so the plants are completely covered with blooms. R.triloba grows 2-5 feet tall and becomes spreading and bushy (up to 4 feet wide) if not crowded by other plants.
R. triloba is nice for mass plantings in the perennial border or naturalizing in the low-maintenance garden. It combines well with ornamental grasses, especially Miscanthus, but also looks good in any informal garden. It makes an excellent cut flower and is well suited to prairie plantings. If not supported by other plants, stake before flowering to keep plants from blowing over.
R. triloba is tolerant of most conditions, but does best in full sun or light shade in sandy, loamy soil. It prefers moderate moisture, but is drought tolerant once established. It is easy to grow from seed, blooming in its second year. Cutting back the flowers just as bloom finishes may help extend the plant’s life. However, these plants readily self-sow, replacing any plants that do not survive. They are ideal in naturalized situations.
– Susan Mahr, University of Wisconsin – Madison