How to Grow Black-eyed Susans

Which black-eyed Susan?

The classic roadside black-eyed Susan is Rudbeckia hirta, native to the prairies and fields of the central and eastern US and now naturalized across most of the country. Sources describe its life span differently: Cornell calls it an annual, Clemson a short-lived perennial best treated as an annual, and NC State a biennial or short-lived perennial. In practice it blooms the first year from early-sown seed, may survive a winter or two, and reseeds freely. The large-flowered, multicolored cultivars are often sold as gloriosa daisies.

For a reliable perennial, choose R. fulgida, orange coneflower, which includes ‘Goldsturm’. It is hardy in zones 3 to 9, peaks from late summer into fall, and can be divided every 3 to 4 years in spring or fall.

Site and soil

Plant in full sun, at least 6 hours a day. Part shade is tolerated. Black-eyed Susans prefer moist, well-drained soil but handle clay, poor soil and drought once established. UF/IFAS notes good salt tolerance, which makes them useful near the beach.

Moderate fertility gives the best flower show. NC State advises against planting where lawn fertilizer will reach, because excess nitrogen works against bloom.

Sowing and planting

Black-eyed Susan is a long-day plant. Wisconsin explains that when days are shorter than about 12 hours, seedlings stay as flat rosettes. Once days are longer than that, they stretch and start to flower. That’s why timing matters: early-sown plants bloom the same summer, while late-sown ones rosette, overwinter and bloom the following year.

Indoors: Sow 6 to 8 weeks before your last frost. Cornell says the seed needs light to germinate, so press it onto the surface or cover it very lightly. Keep it warm. Wisconsin uses 68 to 72°F and gets germination in 10 to 21 days, while UF/IFAS reports 5 to 10 days at 70 to 75°F. Harden seedlings off and plant them out after frost danger has passed. They may wilt for a day or two after transplanting, which is normal.

Outdoors: Sow in early to mid spring. Wisconsin reports success with winter sowing too, scattering seed outdoors before the ground freezes. Clemson also lists early-to-mid fall sowing. Clemson recommends 3 months of cold stratification at 40°F for spring-sown Rudbeckia seed, but Cornell, UF/IFAS and Wisconsin all germinate R. hirta in warmth without chilling. A fall or winter sowing gives the seed natural chilling, so it works with either view.

Spacing: Set plants 1 to 2 feet apart, at the wider end in warm, long-season areas. For a mass planting, UF/IFAS spaces them 18 to 24 inches apart.

Care

Water new plants until they’re established, after which they need watering only in long dry spells. Don’t overfeed. In South Carolina, Clemson suggests a slow-release 12-6-6 fertilizer at about 1 pound per 100 square feet in early to mid April and half that in September, adjusted to a soil test.

Deadheading stretches the bloom season and limits self-seeding. Toward the end of the season, stop deadheading and leave the seed heads. They add winter interest and feed American goldfinches, and the plants reseed for next year. Black-eyed Susan is also a larval host for the silvery checkerspot butterfly.

Bloom timing varies by region and planting date. NC State lists May through July, extended into fall with deadheading, while Cornell lists late summer to mid-fall.

Warm-winter regions

UF/IFAS lists planting months of April-May for zone 9 and March-April or October-November for zones 10-11. The Arizona low desert runs on a different schedule: the University of Arizona chart has seed planted from October through March, with bloom from June into October. The chart lists 120 days to bloom for black-eyed Susan and 60 days for the faster gloriosa daisy strains, which flower from April there.

Varieties

For South Carolina, Clemson lists R. hirta cultivars including ‘Cherokee Sunset’ (brown, red and yellow), ‘Denver Daisy’, ‘Prairie Sun’ and the compact ‘Toto Gold’, 12 to 16 inches and suited to containers and small spaces. Wisconsin describes ‘Prairie Sun’, a 2003 All-America Selections winner with green centers, as thriving in hot, humid summers while also doing well in cooler climates. UF/IFAS highlights ‘Indian Summer’, which flowers 10 to 14 weeks after sowing and doesn’t need staking.

Common problems

• Powdery mildew: the most common disease. Space plants for air flow.
• Leaf spots, fungal and bacterial: encouraged by wet foliage. Remove infected leaves, avoid overhead watering and clear dead plant material.
• Slugs and snails: damage young plants. Protect seedlings early.
• Rabbits: fence with wire at least 2 feet high.
• Aphids, Japanese beetles, spider mites: occasional. Clemson suggests insecticidal soap or horticultural oil if aphids or mites build up.
• Southern blight: a soil-borne disease listed by NC State.
• Goldenglow sawfly and four-lined plant bug: UF/IFAS notes the sawfly larvae can strip plants, and the plant bug’s sunken brown leaf spots are often mistaken for disease.

Black-eyed Susan has been Maryland’s state flower since 1918. The genus honors Olav Rudbeck and his son, both professors at Uppsala, and hirta means “rough-hairy,” which describes the bristly leaves and stems.