Black-Eyed Susans, belonging to the Rudbeckia genus, are bright, cheerful flowers that serve as a dependable presence in many gardens, often thriving as either hardy perennials or self-seeding annuals. These native North American wildflowers are popular for their long blooming season and ability to attract pollinators like butterflies and bees. Increasing the number of these sunny plants in your landscape is straightforward, using two primary methods: propagating new plants from seed or multiplying established clumps through division. Both techniques require specific timing and preparation for successful establishment.
Propagation from Seed
Growing Black-Eyed Susans from seed is an economical way to produce a large quantity of plants. If harvesting from an existing plant, wait until late fall when the central cone, where the tiny black seeds are held, has fully dried out and become a crispy, dark brown. Cut the dried seed heads and let them cure for one to two weeks in a cool, dry place before shaking or crushing the cones to release the seeds.
Successful germination requires a process called cold stratification, which mimics the natural winter conditions needed to break the seed’s dormancy. For indoor sowing, mix the seeds with a small amount of moist material, such as sand or a damp paper towel, and place them inside a sealed plastic bag. This mixture should be refrigerated for a period of about 30 to 45 days to simulate the necessary cold, moist environment.
After the stratification period, sow the seeds indoors approximately six weeks before the last expected frost date in your area. Use a sterile seed-starting mix and lightly press the seeds onto the surface, covering them with only a very thin dusting of soil, as Rudbeckia seeds require light to germinate. Maintain a soil temperature around 70°F and keep the medium consistently moist but not saturated while providing strong light from a south-facing window or grow lights.
Alternatively, direct sow the seeds outdoors in late fall or very early spring, allowing nature to handle the stratification process. Scatter the seeds over a prepared, weed-free area and lightly rake them into the soil surface. Once the resulting seedlings have developed at least five true leaves, they should be gradually hardened off by exposing them to outdoor conditions for increasing periods before transplanting them into their final garden location.
Propagation by Division
Propagating Black-Eyed Susans through division is the fastest method for creating mature new plants and is generally done to rejuvenate existing clumps that have become overcrowded. The best time for division is when the plant is dormant, either in early spring as the new shoots are just beginning to emerge or in the late autumn after the foliage has died back. Dividing in the early spring allows the new sections to establish their root systems before the heat of summer.
Start the division process by thoroughly watering the parent plant the day before to reduce transplant shock and make the soil easier to work. Use a sharp spade to dig a wide circle around the plant’s drip line, which is the imaginary perimeter of the foliage. Carefully lift the entire root ball from the ground, shaking off excess soil to expose the dense root structure.
Younger, newer growth on the perimeter of the clump can often be gently pulled apart by hand, as these sections separate more easily. For the older, woody center of the plant, use a sharp, sterilized knife or two garden forks inserted back-to-back to pry the mass apart. Ensure that each resulting division has a robust cluster of healthy roots and at least three to five visible growing points, sometimes called “eyes,” from which new stems will sprout.
Replant the separated divisions immediately into their newly prepared locations, setting them at the same depth they were growing previously. Spacing the new plants approximately 12 to 18 inches apart will provide adequate room for airflow and future growth, helping to prevent common issues like powdery mildew. Division is typically needed every three to five years when the center of the plant begins to decline and flowering becomes less vigorous.
Establishing New Plants
Regardless of whether propagation began with a small seedling or a large root division, the initial care after planting is important for successful establishment. Immediately after transplanting, thoroughly water the new plants to settle the soil around the roots and eliminate any air pockets. For the first few weeks, maintain a consistent watering schedule, keeping the soil moist but never soggy, until the plant begins to show signs of new, active growth.
Black-Eyed Susans thrive best in a location that receives full sun, meaning at least six hours of direct sunlight each day, though they can tolerate light afternoon shade. The soil should be well-drained, as these plants do not tolerate standing water, but enriching the planting site with compost before setting the plants in place will provide a beneficial boost. A light application of a balanced, slow-release fertilizer at the time of planting can support the development of a strong root system.
To encourage a continuous display of blooms throughout the growing season, remove spent flowers by cutting the stem just below the faded bloom, a practice known as deadheading. In the late fall, resist the urge to cut back the foliage immediately after the first frost, as the remaining stalks and dried seed heads offer insulation for the roots and provide a valuable food source for birds. Wait until early spring to cut the old growth back to the ground, which allows the plant’s energy to be directed into the upcoming season’s new shoots.