Greetings, human observer. I am a Black-eyed Susan (Rudbeckia hirta), and I am here to explain the intricacies of my growth habit from my own perspective. The question of how we spread is fundamental to our existence and our success in painting the late summer landscape in vibrant gold. The simple answer is yes, we do spread, but we do so through a combination of clever strategies.
Our most significant and widespread method of expansion is through our seeds. After our bright yellow or orange rays surround the dark, domed central cone, we undergo a remarkable transformation. Once pollinated by bees and butterflies, that cone fills with hundreds of tiny, elongated seeds. As autumn arrives and our stems dry and turn brown, the cone begins to disintegrate, releasing these seeds to the wind, a process botanists call "self-sowing." A single one of us can produce over a thousand seeds. These seeds do not require special treatment; they simply fall to the ground and, after experiencing the cold dormancy of winter, are ready to germinate with the warmth of spring. This is why you often find new seedlings emerging several feet away from the parent plant, creating a delightful, naturalized look in meadows and gardens.
While many recognize us as short-lived perennials or biennials, we also possess a secondary, slower method of spreading. From our central root crown, we send out underground stems called rhizomes. Think of these as horizontal roots that travel just beneath the soil surface. From nodes along these rhizomes, new vertical shoots are sent up, which develop into full-sized plants. This clonal growth allows a single plant to gradually form a dense clump or colony over a few years. However, it is important to understand that we are not aggressively rhizomatous like Mint or Bamboo. Our rhizomatous spread is modest, typically expanding the clump by a few inches each season. This growth habit makes us excellent for filling in garden spaces without being uncontrollable.
Our life cycle is key to understanding our spreading behavior. Many of us are short-lived perennials, living for a few years, or we complete our life cycle in two years (biennial). In the first year, we focus energy on developing a rosette of leaves at our base. In the second year, we shoot up, flower, set seed, and then the original plant often dies. However, because we have already spread by seed and potentially by rhizomes, our presence continues. This combination of seeding and clumping means that while an individual plant may be transient, the colony we form is persistent and dynamic, constantly renewing itself.
You, humans, are also a significant vector for our spread. Gardeners often collect our seed heads to sow in new areas or divide our clumps in early spring or fall to propagate us. This assisted propagation allows us to travel far beyond the reach of our wind-dispersed seeds. Furthermore, when you plant cultivars of Rudbeckia fulgida, such as 'Goldsturm', you are often introducing a plant that is more strongly rhizomatous than our species form, leading to faster and denser colony formation.
