How to Plant, Grow, and Care for Rudbeckia triloba

Brown-eyed Susan (Rudbeckia triloba) brings waves of sunny yellow flowers that brighten the summer and fall landscape. Cold-hardy, heat-tolerant, and rugged, the native wildflower thrives across growing conditions. R. triloba is similar to its well-known relative, black-eyed Susan (R. hirta), but is taller and has smaller flowers that emerge in profusion later in summer with a longer bloom time. 

Rudbeckia triloba is low-maintenance and adapts to various conditions and soil types. Drought-tolerant once established, it needs little tending to put on a big show from July to October, depending on the climate.

Pollinators appreciate the late infusion of nectar and pollen, while songbirds forage on seeds in fall and winter. For lively color in the border, bouquet, or dried arrangement, brown-eyed Susan shakes away the weariness of late summer.

What is Rudbeckia triloba?

Rudbeckia triloba is a short-lived perennial or biennial with ray flowers. The blanket of bright yellow blooms adds color in late summer until hard frost. Common names include brown-eyed Susan, thin-leaved coneflower, and three-lobed coneflower.

The natives spend the first year developing roots and leafy growth and may produce some flowers. In the second year, full-flowering glory sweeps in before they fade. With easy reseeding, spring yields a successional crop of color.

Rucbeckia triloba is at home in the ornamental border and in native, wildflower, pollinator, rock, and cottage gardens. They’re showy en masse, which is easy to achieve with ready reseeding. They also make a vibrant addition to fresh florals that last a long time in the vase.

Brown-eyed Susan is a host plant for the silvery checkerspot butterfly (Chlosyne nycteis) and supports other pollinators and beneficial insects with their pollen and nectar. Songbirds, especially American goldfinches, forage on the seeds in the cool season.

Characteristics

Late summer and fall see a blanket of golden daisy blooms, persisting until hard frost. Multibranched stems create the all-over bloom coverage as they rise above basal leaves. Allowed to spread without other plants nearby, the bushy mounds reach four feet wide.

Each bright bloom measures one to three inches across and appears in a mass at full bloom. Short, flat, and wide, the petite flowers hold 8 to 12 rays. Black button centers fade to dark purple-brown before producing seeds and drying.

The dark green basal leaves have three divided oval lobes (hence the species name triloba). The leafy rosettes may persist through winter as an evergreen groundcover. 

Cluster brown-eyed Susan with other perennials to support the tall stems in flower. They pair beautifully with ornamental grasses and with other blooms like aster, monarda, echinacea, columbine, lupine, and amsonia.

Native Area

R. triloba is native to the Midwest and Eastern regions of the U.S., from New York to Florida and west to Minnesota, Texas, and Utah. Its natural habitat is moist, open woods, fields, along streams, and on rocky slopes.

With hardiness across USDA zones 3 through 9, the perennials bear good heat and cold tolerance in wide-ranging growing situations. 

Planting

The wildflowers reseed to expand the colony and fill a space given the chance. Space them 12 to 18 inches apart to allow ample air circulation while presenting a dense display of the basal leaves and multi-branched stems. In windy or shady zones, the tall stems may need support to keep from falling over. While they can reach five feet, two to three feet is more common.

Transplanting 

Heat-loving brown-eyed Susan develops quickly in warm temperatures with peak bloom from June or July through frost. Direct sow seeds or transplant seedlings after the final frost as soil and air temperatures warm. To get a jump start on growth, start seeds indoors six to eight weeks before the last anticipated frost date. 

How to Grow

The low-maintenance wildflowers tolerate a range of conditions and need few extra resources. They benefit from average moisture and full sun for best growth and flowering, but adapt to lesser situations.

Light

Thin-leaved coneflower performs best in full sun, with six or more hours of sunlight daily. It tolerates partial shade (about four or more hours), especially in areas with intense afternoon sun.

The adaptable native thrives across exposures, with more sun allowing increased growth and flowering. Those in more shade may have floppy stems that require support.

Water

The flowering perennial shows the best color with regular water. Consistent moisture during the growing season ensures overall health and a profusion of blooms, though the plants are drought-tolerant once established.

While they tolerate dry spells, they won’t withstand soggy soils. Avoid prolonged wet conditions, as oversaturation leads to weakness and potential fungal diseases like powdery mildew.

Soil

Loose, sandy, loamy soils are best for Rudbeckia triloba. It adapts to a wide range of types and textures as long as they’re well-draining. Good drainage is essential for staving off oversaturation and for roots to thrive.

At planting, topdress with compost over the entire area, especially in poor soils like clay and sand. The organic material aids in aeration, moisture retention, drainage, and nutrition. 

Temperature and Humidity

The durable wildflower tolerates heat and humidity up to zone 9 and sometimes 10, as well as cold winters in zones 3-4. Their semi-evergreen basal leaves persist through winter in mild zones.

Provide proper spacing for good air circulation in climates with moderate, humid summers to prevent mildew problems. Prune surrounding plants as they grow if more space or airflow is beneficial.

Fertilizing

Aside from compost to boost nutrition and drainage in poor soils, there’s no need for additional fertilizer for three-lobed rudbeckia to flourish.

Maintenance

Cutting back stems after flowering can extend the plant’s longevity as it doesn’t direct energy into seed production. Deadheading may also promote additional blooms and prevent unwanted seeding, too. To allow reseeding and forage for songbirds, leave blooms intact at season’s end.

Let the basal rosettes remain in place over the winter as insulation, and remove any ragged leaves in spring to make way for new growth.

Propagation

The short-lived perennials naturalize through self-seeding and propagate easily with direct sowing. Let the seeds disperse on their own, or wait at least three to four weeks after flowering to collect them. They turn dark gray when mature. Waiting a little longer makes for easier collection with looser cones.

Rudbeckia triloba benefits from cold stratification for the best germination. As seeds disperse naturally, they’ll experience a chill period in winter for emerging in spring. For indoor seed starting, store them in the refrigerator in a baggie or an airtight container in moist sand or a paper towel for one to three months. Then plant them in seedling trays.

Growing From Seed

Direct sow seeds in fall to give them their cold, moist period. Or, pre-chill them and start them indoors six to eight weeks before your final frost date for earlier establishment, transplanting after the danger of frost passes. 

Winter sowing is another viable seed-starting method for R. triloba, with easy seeding in protective containers outside to receive natural cold stratification.

Common Problems

Brown-eyed Susan doesn’t have many pest or disease issues. Slugs and snails may visit young seedlings. The fungal disease powdery mildew may be an issue in cool, humid weather.

Pests

Slugs and snails feed on soft shoots and tender new growth, especially early in the season. They’re most active in cool, damp conditions in the evening and early morning. You’ll notice irregular holes in leaves and their silvery, sluggy trail.

Hand-pick slugs and snails with scouting during their active times. In the middle of the day, they hide under leaves, mulch, and soil. Lure them with lettuce leaves or citrus rinds and collect them in the morning. If numbers increase, bait them with beer or soda traps by filling a shallow dish and placing it at soil level.

Diatomaceous earth scattered around the base of the stems contains sharp particles that harm soft-bodied creatures as they crawl. It needs reapplication after heavy rains to maintain the boundary.

Remove mulch from around the crown to limit protective hiding spots. Target irrigation at the root level to reduce damp conditions, which are an inviting habitat for the gastropods.

Diseases

Powdery mildew sets in as the pathogen Erysiphe spreads as a grayish-white dust on leaves, buds, and stems. Leaves may turn yellow, distort, and drop during severe infections. Fortunately, powdery mildew is treatable with early detection.

Horticultural oils like neem can treat the fungal disease early on. To prevent the occurrence, take care not to overwater or overfertilize, which weakens the coneflowers and increases disease susceptibility.

Space them to allow ample airflow, and follow proper watering to avoid wetting the leaves unnecessarily. Remove diseased leaves and any fallen debris to prevent harboring the spores.

Frequently Asked Questions