Sweet Black-eyed Susan in full flower at LeRoy Oaks Forest Preserve, Kane County Forest Preserve District. Each flower is 2-3 inches across.
Sweet Black-eyed Susan growing next to taller Cup Plant (Silphium perfoliatum). The latter is about 6-7' tall. This image, taken 8/9/2017 shows the mature height of each plant.
Sweet Coneflower/Sweet Black-eyed Susan (Rudbeckia subtomentosa)
by Trish Beckjord, RLA
While I hesitate to write about taller native plants as typically being too oversized for a residential garden, this is one species that I’ve decided I just have to mention. Growing 3-6’ tall, with a fibrous (and rhizomatous!) root system, this lovely summer native blooms mid- to late summer for 4 to 6 weeks and is now in its full glory. Flowers of golden-yellow “petals” (ray flowers) and dark center disc flowers look very similar to its shorter – and shorter-lived – cousins, Black-eyed Susan (Rudbeckia hirta) and Showy Black-eyed Susan (Rudbeckia fulgida var. speciosa). Over time, each plant will expand to form larger multi-stemmed clumps.
This Rudbeckia species is called “Sweet” for its pleasant fragrance when it is in bloom. Many describe it as similar to Sweet Grass (Hierochloe odorata). I only know that a walk in the prairie when it is in flower is wonderful! I often just stop and breathe in the fragrance of the air!
Sweet Black-eyed Susan is a tough perennial that doesn’t need or want amended garden soils which will only encourage it to grow taller and topple over. Rather, this species prefers loam or sandy-loam soils in full sun with moist to average soil moisture. It will also tolerate a higher clay soil content and some shade although it will not bloom as effectively in lower light conditions. Once established it is drought tolerant, and its hairy stems and leaves make it resistant to munching by deer and rabbits. Consider this species for rain garden and bioswale plantings.
Sweet Black-eyed Susan has high wildlife value. Nectar and pollen attract a wide variety of bees and flies, skippers and small to medium sized butterflies among other insects. According to Illinois Wildflowers, bees are the most important pollinators. One, Heterosarus rudbeckiae, is a specialist pollinator of Rudbeckia species. Sweet Black-eyed Susan is also a host plant for caterpillars of the Silvery Checkerspot butterfly and several moth species.
This Rudbeckia is the species of origin for the cultivars Rudbeckia subtomentosa ‘Henry Eilers’ and a shorter selection ‘Little Henry.’ Flowers in the ‘Little Henry’ selection are of similar appearance to ‘Henry Eilers’. For more on how to differentiate between the Rudbeckia species R. hirta, R.fulgida and R. subtomentosa, the reader is referred to the description of this species in Dr. John Hilty’s Illinois Wildflowers website at www.illinoiswildflowers.info.
Author’s Note: I have grown another Rudbeckia species, Brown-eyed Susan (Rudbeckia triloba), in my garden and found it reseeds much too aggressively for me to ever recommend it for residential use. This may be due to its being a shorter-lived perennial and the fact that it prefers disturbed ground. Please let me know if any of you have found Rudbeckia subtomentosa similarly invasive as there is nothing in the literature that mentions this and I will pass it along. Thanks!