Black Eyed Susans (Rudbeckia) generally reseed themselves vigorously in the garden. These ornamental flowers are popular for their bright yellow petals and dark centers, but their ability to self-sow is a reason for their widespread presence. This characteristic allows them to naturalize easily in many different settings, giving the appearance of a persistent, returning flower. While this self-seeding behavior is welcomed by many gardeners for creating dense, wildflower-style plantings, it can also lead to the plants spreading beyond intended areas.
How Black Eyed Susans Propagate
The mechanism for the Black Eyed Susan’s return is found in the spent flower heads, which develop into seed-bearing cones. As the summer bloom fades, the central cone dries and matures, housing hundreds of tiny, viable seeds. One single plant can produce more than a thousand seeds, ensuring the next generation has a high chance of success.
The timing of seed dispersal occurs in late fall or early winter as the dried seed heads shatter. These seeds fall directly onto the soil surface beneath the parent plant, or they are scattered by wind or foraging birds, particularly goldfinches, who consume the seeds during the cold months. For successful germination, the seeds require a period of cold, moist conditions, a process known as cold stratification, which mimics the natural winter cycle. This cold period breaks the seed’s dormancy, preparing it to sprout when soil temperatures warm up in the spring, ideally reaching around 70°F.
Annual Versus Perennial Varieties
The specific life cycle of the Black Eyed Susan influences reseeding. The most common species, Rudbeckia hirta, is technically a biennial or a short-lived perennial. This type relies almost entirely on self-seeding to ensure its continued presence year after year, as the parent plant often dies after its second year of flowering. Varieties like ‘Gloriosa Daisy’ fall into this category and must reseed to return to the garden.
In contrast, true perennial varieties, such as Rudbeckia fulgida (often seen in the form of ‘Goldsturm’), return each year from their established root crown. They also produce seeds and self-sow as a secondary method of spread. Rudbeckia fulgida can spread through underground stems called rhizomes, which can cause the plant clump to expand and overtake nearby areas. Understanding the species is important, as annual types must reseed to survive, while perennial types use reseeding for broader colonization.
Encouraging and Controlling Reseeding
Gardeners can manage Black Eyed Susan populations by either encouraging or preventing reseeding. To promote reseeding, leaving the spent flowers on the plant in the late season is the most effective approach. Allowing the flower cones to fully mature and dry on the stem ensures the seeds are viable and ready to drop naturally throughout the fall and winter. These dropped seeds will then undergo cold stratification outdoors to germinate the following spring.
To control or prevent the plant from self-sowing excessively, the practice of deadheading is necessary. Deadheading involves removing the spent flowers before the seeds in the cone fully mature and disperse. This physical removal of the seed source limits the number of new volunteer seedlings that appear the next year. Applying a layer of mulch around the base of the plants can also inhibit the germination of any seeds that fall onto the soil, as mulch blocks the light that the seeds need to sprout.