Plant taxonomy classifies black-eyed Susans as Rudbeckia hirta.
These distinctions are sometimes lost on the casual observer since the plants re-seed readily: if you see the seedlings sprouting up in the same place year after year, you could easily gain the impression that you have a perennial (even if you do not, in fact, have a perennial type).
Black-eyed Susans are valued as long-blooming perennials, putting out numerous flowers non-stop for most of the summer and into early autumn. The cheerful flowers consist of golden petals that radiate from a dark cone (thus the common name, even though the color is more of a dark brown). Small hairs cover the stems and leaves, accounting for the specific epithet, hirta (Latin for "hairy"; think "hirsute"). When in bloom, black-eyed Susans stand two to three feet tall, with a spread of up to two feet.
It is difficult to say if the best feature of these plants is the abundance of their flowers or the fact that they bloom for such a long time. But, the latter quality is especially appealing: plant black-eyed Susans in a corner of your garden, and for half of the growing season, you're sure to have color there. Moreover, native-plant aficionados in North America will be drawn by its indigenous status to consider it as a candidate for native plant perennial sun gardens.
Planting Zones, Sun and Soil Requirements
Plant in full sun (or partial sun in the South) and in soil of average fertility. Plants will spread more in a friable soil than in clay (which may or may not be desirable). These cheerful plants are drought-tolerant perennials once established but perform better if watered during dry spells.
Uses in Landscaping, Care for Black-Eyed Susans
Black-eyed Susans are often massed together in perennial borders and are effective at erosion control. Like 'Becky' shasta daisies, they also make fine cut flowers. Popular in wildflower gardens, this is one type of wildflower that almost everyone knows, even non-plant lovers.
Black-eyed Susans are susceptible to powdery mildew. To prevent an infestation, keep your Rudbeckia flowers thinned out. If the powdery mildew is already present, treat with a fungicide. Black-eyed Susan flowers can also profit from deadheading. To propagate and/or rejuvenate, divide in spring.
Other Types of Rudbeckia Flowers, Confusion Caused by Common Names
There are many types of Rudbeckia flowers, another popular species being fulgida. Many grow the cultivar, 'Goldsturm' (Rudbeckia fulgida var. sullivantii 'Goldsturm').
Rudbeckia flowers are sometimes referred to as "coneflowers," but that common name is more typically applied to Echinacea, which includes the coneflowers such as the old standby, purple coneflower (Echinacea purpurea) and newer types such as the orange coneflower. While related, plants in the Echinacea genus are a distinct group from those in the Rudbeckia genus. Such common names can be confusing, which is why scientific plant names are used when specificity is paramount.
Another common name that can create some confusion is "Gloriosa daisy." Sometimes used synonymously with "black-eyed Susan," you may want to restrict its usage to references to Rudbeckia hirta 'Gloriosa.' The latter has bi-colored flowers ("tri-colored" flowers if you count the central cone):
- A dark cone stands at the center.
- A rust-colored ring surrounds this cone, at the base of the petals.
- The remaining 2/3 of each petal is golden