Black-eyed Susan

Identification and origin

Rudbeckia hirta belongs to the family Asteraceae. It is native to North America, where it grows wild across most of the United States and in southern Canada, from Ontario to Saskatchewan. It occurs in open woods, prairies, fields, roadsides, and waste ground.

It is a fast-growing annual, biennial, or short-lived perennial. In spring it first forms a rosette of oval basal leaves, sometimes toothed, the larger ones tapering into long stalks. The upright, branching, grooved stems then carry lance-shaped leaves 3–7 in long. Stems and leaves are covered in short, stiff hairs that make them rough to the touch: that is the meaning of the epithet hirta, “hairy.” The plant grows 12 in – 4 ft tall and 12 in – 2 ft wide.

The flower heads, up to 3 in across, have ten to twenty bright yellow to orange-yellow rays around a domed, chocolate-brown or sometimes greenish center. They open from summer to mid-fall, especially if you deadhead, and make excellent, long-lasting cut flowers. They attract butterflies and pollinators; American goldfinches eat the seeds in fall, and the plant feeds the caterpillars of several butterflies and moths. Deer tend to leave it alone.

The genus honors Olof Rudbeck, the Swedish botanist who founded the Uppsala Botanic Garden, where Linnaeus was professor of botany.

The very large-flowered cultivars, often sold as gloriosa daisies, come in red, bronze, orange, and bicolors: ‘Indian Summer’ (yellow flowers 6–9 in across), ‘Cherry Brandy’ (cherry red), ‘Denver Daisy’ (a large mahogany eye), ‘Prairie Sun’, ‘Cappuccino’, and the dwarf ‘Toto’, about 10 in tall.

Light

Give it full sun, at least six hours a day: that is where it blooms best. It tolerates light part shade, but the shadier the spot, the fewer the flowers. As a prairie plant, it handles windy, exposed sites well.

Watering

It prefers medium moisture and dislikes drying out during the growing season, although it tolerates drought better than most other rudbeckias. In the ground, water during long dry spells or on very free-draining soil: a deep soaking now and then is better than frequent small sips. The soil should stay slightly moist, never soggy.

In a container, the mix dries out much faster: check it often and water as needed, sometimes daily in hot weather, without letting it dry out. A summer planting also needs more regular watering to keep the root ball moist.

Potting mix

Undemanding, it grows in average, moist, well-drained soil, whether clay, loam, or sand, acidic to alkaline. It does best in humus-rich soil that holds moisture in summer, but it dislikes poorly drained soil that stays waterlogged, especially in winter.

Moderate fertility gives the best bloom: avoid lawn edges, where lawn fertilizer supplies too much nitrogen. A mulch of well-rotted compost in spring is usually enough. On very sandy soil, a general-purpose fertilizer as growth begins helps; in containers, use a liquid fertilizer diluted according to the label.

Temperature

The species is hardy in USDA zones 3a to 8b and handles heat well. In British gardens, by contrast, it rarely survives the winter except in the mildest areas: there it is treated as a half-hardy annual and sown each year. You can try overwintering a plant in a bright, frost-free greenhouse and replanting it in late spring.

Spring seedlings started indoors go outside only after the last frost, once they have been gradually hardened off to outdoor conditions.

Repotting

Plug plants are first potted up into 4 in pots, then hardened off before planting out after the frosts.

It also does well in containers and window boxes with drainage holes. Since it lives only a few years and is usually grown as an annual, repotting is rarely worthwhile: in late fall, compost the plants and start again from seed in spring.

Pruning

Deadhead regularly: the plant produces new blooms, and you avoid excessive self-seeding. Cutting flowers for bouquets has the same effect.

At the end of the season, you can let a few flower heads go to seed: their cones add winter interest, feed birds, and ensure reseeding. Pull out spent plants in late fall.

Propagation

Black-eyed Susan is grown from seed. Indoors, sow in late winter or early spring, thinly, in a tray of moist, peat-free seed-starting mix. The seeds need light to germinate: barely cover them. Keep them at about 68 °F under a propagator lid until they sprout, then harden off the seedlings before moving them outside.

You can also sow directly in the garden around the last frost date or in late spring. Plants bloom in their first year. Once established, it reseeds freely and persists in the garden that way, even when the original plants die out.

Common problems

• White powdery coating on leaves: powdery mildew, especially on dry soil.
• Chewed leaves and young shoots: slugs and snails, particularly on young plants.
• Clusters of insects on shoots: aphids.
• Leaf and bud nematodes: occasional pests.
• Few flowers: too much shade, excess nitrogen, or no deadheading.
• Plants that vanish after one or two seasons: normal for this short-lived species.

A symptom can have several causes: also look at watering, drainage, and exposure before treating.

Toxicity

Veterinary and medical references report no toxicity for this species: it does not appear among the plants listed as toxic to dogs and cats. Still, don’t let children or pets eat garden plants, and contact a professional if a large amount is eaten or an unusual reaction occurs.