Black-Eyed Susan can be perennial (Rudbeckia fulgida) or annual (Rudbeckia hirta). Garden varieties of both have been bred from wildflowers that are common throughout the United States and southern Canada.
If you don’t mind some untidiness in your winter garden, and if you like to feed the birds, don’t bother removing dead foliage and cutting stalks back. Birds will feast on the seeds.
Perennial Black-Eyed Susan is hardy, especially if you give it a light mulch of dried leaves—mimicking the way leaves would catch in the flower stalks if the plant grew wild. Annual Black-Eyed Susan self-seeds, so new plants will appear in the spring. Keep the surrounding ground bare, so seeds have a place to rest through the winter and sprout in the spring.
If you cut back stalks of perennial Black-Eyed Susan, wait until late fall when the plant is completely dormant. Leave three or four inches of the stem above the basal leaves to avoid injuring the plant. Cover the plant well with a mulch of dried leaves, especially in the first year after planting or dividing.
If you cut back stalks of annual Black-eyed Susan, it will not be able to self-seed. Lay the stems with the seed heads on a paper plate and let them dry. Shaking or rubbing the dry seed head will release the seeds onto the paper plate. You can store them through the winter in a labeled envelope or plastic bag and plant in the spring.