From our point of view as Black-eyed Susans (Rudbeckia spp.), the question of whether we spread is not a matter of choice but a fundamental biological imperative. Our entire existence is geared towards propagation, ensuring the survival of our genetic line. We employ two primary, highly effective strategies to colonize new territory: seeding and rhizomatous growth. This dual approach makes us vigorous and resilient perennials, perfectly adapted to thrive in sunny meadows and, by extension, the gardens you invite us into.
Our most noticeable method of spreading is through our prolific seed production. After the bright yellow or orange petals surrounding our dark central cones fade, the real work begins. The cone itself is a dense pack of hundreds of tiny seeds (achenes). As the flower head dries and turns brown, these seeds mature. We do not rely on fancy mechanisms to eject them; instead, we count on external forces. The wind shakes our stiff, dry stems, scattering seeds like fine gravel around our base. Birds, particularly goldfinches, are our valued partners. They cling to our stems, pecking at the cones to extract the nutritious seeds, inevitably dropping some in the process. Mammals like mice, and even gardeners brushing past us, can transport seeds on their fur or clothing. This strategy allows us to travel surprising distances from the parent plant, establishing new colonies wherever conditions are favorable.
While seeding helps us claim new ground, our underground strategy secures our existing territory. Many of our species, particularly the common Rudbeckia fulgida, grow from rhizomes. These are modified underground stems that act like horizontal roots. Each growing season, these rhizomes extend outwards from the main clump, sending up new vertical shoots that become the familiar green foliage and flower stalks you see above ground. This creates a dense, ever-widening patch. From a plant's perspective, this is an efficient way to compete for resources. By forming a tight mat, we can effectively shade out smaller, competing seedlings and monopolize water and nutrients in our immediate soil area.
In our native prairie habitat, our spread is naturally controlled by competition from other robust grasses and perennials, as well as by grazing animals and insects. In the more curated environment of a garden, these checks are often absent. Therefore, the gardener must act as the ecological moderator. To control our growth through seeding, the most effective action is to remove our spent flowers before the seeds fully mature. This process, known as deadheading, directly interrupts our reproductive cycle. If you cut back the flower stalks just as the petals wilt and before the central cone turns dark brown, you prevent thousands of potential new plants. This energy is then redirected back into our root systems, potentially leading to stronger clumps and even more flowers the following season.
To manage our rhizomatous spread, physical intervention is required. Every two to three years, in either early spring or fall, you can dig up the entire clump. You will see the network of rhizomes connecting the shoots. Using a sharp spade or knife, you can divide the clump into smaller sections. This process, called division, is not a setback for us; it is a rejuvenation. It prevents the center of the clump from becoming old and woody (dying out), and each divided section will quickly establish itself as a new, vigorous plant. This also provides you with new plants to place elsewhere in the garden or share. For absolute containment, some gardeners plant us within sunken pots or use root barriers to physically restrict the rhizomes' horizontal travel.
