Rudbeckia are perennial flowering plants that are hardy in Zones 4–9. Like many plants, they have several common names, among which are: Black-eyed Susan, Gloriosa Daisy, and Yellow Ox Eye. They are members of the Asteraceae family and are native to both damp woodlands and dry prairies in North America. Most are considered perennial; however, there are some annual species, such as R. hirta. Species that are commonly available are R. hirta, R. fulgida, R. grandiflora, and R. triloba.
Rudbeckia have erect stems with alternate, deeply lobed pubescent (hairy) leaves. The leaves are coarse and sometimes feel like sandpaper. Plants are clump forming and produce colonies via rhizomes (underground stems). The showy flowers are approximately 2–3 inches in diameter with ray-like petals and a flat, dark eye center.
Rudbeckia species have an average growth rate and prefer full sun (greater than 6 hours of direct sunlight) but will tolerate partial shade. Rudbeckia prefer evenly moist, well-drained soils, but they are drought and heat tolerant once established. They can also adapt well to average soils.
Rudbeckia have a clumping, but upright habit, and coarse texture. Black-eyed Susans will average 2–3 feet in height and about 1–2 feet in clump width. However, colonies of Black-eyed Susans can become quite large. Proper spacing between plants will increase air circulation between the plants to keep leaves dry and help prevent the spread of diseases.
Black-eyed Susans are moderate feeders. In the absence of a soil test, they can be maintained with an application of a 12-6-6 slow release fertilizer at a rate of 1 pound per 100 square feet in early to mid-April, when new leaves begin to emerge, and again in September at a ½ pound per 100 square feet. In most cases supplemental calcium via bone meal will be necessary to provide full nutrition. Test the soil in the landscape bed through Clemson Cooperative Extension for the amount of lime required and the best fertilizer to apply. There are many areas in the lower part of the state where phosphorus levels are naturally high, so a soil test will determine if adding a fertilizer with phosphorus is necessary or not. Excess nitrogen and phosphorus in water runoff can also lead to potential cyanobacteria algal blooms in ponds and lakes.
Early fall is the best time to plant perennial Rudbeckia, but they can also be planted in mid-April. If planted in the fall, the plants will have adequate time to acclimate to their new environment. For more information on planting, see fact sheet HGIC 1153, Growing Perennials.
Once Rudbeckia is established in the landscape, dead foliage and stems can be removed in the fall, winter, or early spring. Deadheading old flowers will encourage re-blooming and keep the plants looking their best. Black-eyed Susans typically bloom in late spring through early fall. Annual Rudbeckia are planted in spring after the last chance of frost.
Rudbeckia’s upright growth and coarse texture makes it ideal for mass plantings in naturalized areas or in the background of perennial beds. The showy flowers will attract bees, butterflies, and the seeds are loved by birds. Additional insects that Rudbeckia will attract are hover flies and minute pirate bugs. These insects are very good natural predators of garden pests, such as thrips, aphids, and whiteflies.
Rudbeckia also make excellent cut flowers for arrangements due to their bright color and strong stems. Their drought resistance and low maintenance make them an excellent addition to a water-wise landscape, raingarden, or xeriscape.
Propagation & Division
Rudbeckia can be propagated by seed, but the best way to propagate them is by division.
Seed: If propagating from seed, sow seeds in early to mid-fall, or early to mid-spring. Seeds sown in the spring will need to be stratified (subjected to a cold treatment to mimic winter conditions) for 3 months at 40°F. Cover the seeds lightly with ¼ to ½ inch of soil and keep moist. Germination should take about 2 weeks. Seeds can be sown indoors up to 2 months before frost; however, it may take 2 years or more to develop a sizeable plant.
Division: Rudbeckia can be divided every 3–4 years in early spring or fall to prevent overcrowding. For more specific information on how to divide Rudbeckia, see fact sheet HGIC 1150, Dividing Perennials.
Diseases: Rudbeckia are infrequently subject to several disease problems, such as powdery mildew, bacterial leaf spots, fungal leaf spots, stem rots, downy mildew, and fungal rusts. All of these pathogens are typically encouraged by excess moisture on the leaves (usually after frequent rain or overhead irrigation), so cultural practices, such as proper spacing to encourage air movement, the removal of dead plant material, and utilizing drip irrigation will reduce the risk for infection.
Rudbeckia spp. can also be subject to some viruses and phytoplasma diseases which will cause deformed flowers or leaves. If any of these pathogens are identified, it is best to remove and destroy the affect plant material, as there is no cure.
Aphids: There are several naturally occurring predators that aid in the control of aphids, among which are green lacewing larvae and parasitic wasps. If an insecticide is necessary for control, use a spray of horticultural summer oil or insecticidal soap. Be sure to read and follow all label directions before use. For more information on insecticidal soap treatments see fact sheet HGIC 2771, Insecticidal Soaps for Garden Pest Control.
Caterpillars: Caterpillars will cause damage, but it is usually minor. Natural predators can be attracted, but the best treatment is any product containing Bt (Bacillus thuringiensis kurstaki). Most Bt products are sold under the trade name Thuricide.
Japanese Beetles: Most natural enemies of Japanese Beetles will be mammals that eat the larvae or grubs, such as opossums, raccoons, and skunks. However, since these can be pests themselves by digging up the lawn, it is best to prevent them with any product containing Bacillus papillae, such as Milky Spore. Apply this product during the summer can help reduce the number of Japanese Beetle grubs.
Two-spotted spider mites: There are many naturally-occurring biological control measures, such as predatory mites (Amblysieus swirskii, Amblysieus californicus, Amblysieus cucmeris, and Phytoseiulus persimilis). These mites naturally feed on two-spotted spider mites and will provide adequate management if the spider mite populations are relatively low. However, if spider mite populations are high, use a spray of horticultural summer oil or insecticidal soap. Be sure to read and follow all label directions before use.
Species & Cultivars
Rudbeckia fulgida is a tried and true species that has large lance-shaped basal leaves and grows to 2–3 feet in height and 2 feet in width. This species typically flowers in mid- to late summer through mid-fall.
Rudbeckia fulgida cultivars:
- ‘City Garden’ is a dwarf version that only grows to 10–12 inches high and spreads 16–18 inches; it is ideal for container gardening.
- ‘Goldsturm’ grows to 23–29 inches in height and spreads 18–23 inches.
- ‘Little Goldstar’ grows to 14–16 inches in height and spreads 14–16 inches; it is ideal for container gardening.
Rudbeckia grandiflora is a rhizomatous perennial species native to the Eastern United States. The plant is huge, growing to 39–47 inches in height and spreading 23–29 inches. Colonies of this species can be quite large, covering massive areas. The flowers are a bright and showy yellow and make perfect cut flowers and are attractants for pollinators and beneficial insects.
Rudbeckia hirta is a short-lived perennial that should be treated as an annual. It may likely endure few winters, but will often self-seed prolifically. The flowers are showier than other Rudbeckia species and have been widely hybridized.
Rudbeckia hirta cultivars:
- ‘Autumn Colors’ grows to 20–23 inches in height and spreads 12–18 inches. The flowers are a dark mix of bronze orange and red. The variety makes an excellent addition to any garden.
- ‘Cherokee Sunset’ grows to 27–29 inches in height and spreads 12–16 inches. This variety is simply stunning. The flower has a mix of brown, red, and yellow, and makes excellent cut flowers or specimen plantings.
- ‘Denver Daisy’ grows to 18 – 20 inches in height and spreads 12 – 18 inches. The flower is unique, having yellow petals with a dark brown center and a mahogany eye.
- ‘Goldilocks’ grows to 20–23 inches in height and spreads 12–18 inches. The yellow flowers are large and showy. They make excellent cut flowers.
- ‘Goldrush’ grows to 18–23 inches in height and spreads 18–23 inches. This showy variety is ideal for use as cut flowers.
- ‘Prairie Sun’ grows to 27– 31 inches in height and spreads 12–16 inches. The flowers are bright yellow with greenish yellow centers.
- ‘Rustic Colors’ grows to 18–23 inches in height and spreads 12–18 inches. The flowers are a mix of orange and bronze with yellow edges.
- ‘Sonora’ grows to 12–16 inches in height and spreads 12–18 inches. The flowers have large dark brown centers with yellow edges.
- ‘Toto Gold’ grows to 12–16 inches in height and spreads 10–12 inches. With its classic yellow showy flowers with black centers, it is perfect miniature Rudbeckia species for small garden areas or containers.
- ‘Toto Lemon’ grows to 12–16 inches tall and spreads 10–12 inches. This variety is ideal for small gardens, containers, and as cut flowers.
Rudbeckia triloba is a species native all over the eastern North America. The species is a short-lived perennial that will self-seed and works well in naturalized areas. The bright yellow flowers have a dark black center and are a great addition to compliment native plantings.
Other Related Species
Rudbeckia laciniata is affectionately known as the “Out House Plant”. The large yellow flowers have a whimsical look and make excellent cut flowers or even a good choice for a children’s garden or fairy garden.
Rudbeckia maxima is species native to the Southern United States. It blooms in mid-summer through mid-fall with large, 3 inch yellow flowers and black centers. The leaves grow more upright, which gives the plant a different look than other Rudbeckia species.