From our perspective as Black-eyed Susans (*Rudbeckia hirta*), the question of "spreading" is not one of invasion, but of survival and prosperity. Our entire biological programming is geared towards propagation, ensuring the continuation of our lineage. We employ two highly effective, natural strategies to colonize space in the garden: prolific seeding and rhizomatous expansion. To understand how to control our growth, you must first understand these innate drives that define our very existence.
Our most significant contribution to spreading is through our seeds. Each of our distinctive, dark-centered flower heads is not a single flower, but a composite of hundreds of tiny individual florets. After the vibrant yellow petals (ray florets) attract pollinators like bees and butterflies to the central cone (disk florets), each successfully pollinated floret develops into a single, small, dry seed. A single flower head can produce a staggering number of seeds. These seeds are equipped with a modest, bristly pappus that allows them to be dispersed short distances by wind, but more commonly, they simply drop to the ground around the parent plant. They are also spread by birds, particularly finches, who relish the seeds. Once on the soil, many seeds will germinate the following spring, creating a dense cluster of seedlings around the original plant. This is why you often find us growing in substantial clumps or colonies.
While often described as clump-forming, many of our perennial varieties, such as *Rudbeckia fulgida*, possess a secondary spreading mechanism: underground stems called rhizomes. These rhizomes are modified stems that grow horizontally just beneath the soil surface. From nodes along these rhizomes, new vertical shoots emerge, developing into what appears to be a separate plant, but is genetically identical to the parent—a clone. This vegetative reproduction allows us to steadily increase the girth of our clump year after year. It is a slower, more deliberate form of spread than seeding, but it is highly effective at securing territory and outcompeting neighboring plants for resources like water and nutrients.
Controlling our growth is a matter of respectfully interrupting our natural reproductive cycles. It does not require fighting our nature, but rather, guiding it.
The single most impactful action you can take is deadheading. By removing our spent flower heads before the seeds mature and disperse, you directly prevent the next generation of volunteers from appearing. Simply snip off the flower stem down to the next set of leaves. This practice not only controls our spread but also encourages us to put energy into producing more blooms rather than seeds, potentially extending our flowering period. If you wish to have a few new plants, you can allow the last flowers of the season to go to seed, providing food for birds and ensuring some natural regeneration.
For perennial varieties that spread via rhizomes, periodic division is the key to control. Every three to four years, in either early spring or early fall, you can dig up the entire clump. Using a sharp spade or knife, you can slice through the root mass to divide it into smaller sections. This process mimics a natural disturbance and is actually beneficial to us, as it rejuvenates older, crowded centers that may have begun to die out. You can replant a division or two in the original location and share, relocate, or compost the remainder. This is an excellent way to manage our size and propagate us intentionally.
Another method is to work with our habits in your garden design. Planting us in areas where we have natural boundaries, such as against a path, a wall, or in a raised bed, can physically contain our rhizomatous spread. Alternatively, you can install a vertical edging barrier sunk about 6 inches into the soil around the planting area to block the advance of the underground rhizomes. This creates a defined space for us to thrive without encroaching on our neighbors.
