Rudbeckia hirta is a variable species that provides a splash of color in the summer garden with its brightly-colored yellow, gold, and mahogany blooms. Native to the plains and prairies of the Midwest, R. hirta is now naturalized throughout most of the continental United States and southern Canada, occurring in open woods, prairies, fields, and roadsides. Plant breeders have developed numerous variations on the typical daisy flower. These cultivated strains (often called gloriosa daisies) generally have larger or more richly colored petals than the species. ‘Prairie Sun’ is an unusual selection of R. hirta bred in Germany, with a light green eye instead of the typical dark brown central disk flowers of the species. This special cultivar was unique and tough enough to be both a 2003 All-America Selections winner and a Fleuroselect Winner in Europe.
‘Prairie Sun’ has large flowers from mid-summer through fall. Butterflies and soldier beetles are common visitors to these flowers. The single flower heads are 5” in diameter, with gold ray flowers (petals) and a light green, button-like center. The petals are a rich golden-yellow-orange at the base and soften to lemon-yellow at the edge. This color pattern is very consistent, giving the plant a more formal look than some other R. hirta cultivars that have great variability in flower patterning and/or colors. The durable plants grow about 3 feet tall, providing color for many weeks. The flowers are borne on long, sturdy branching stems, making it an excellent, long-lasting cut flower. It blooms slightly later than the similar cultivar ‘Irish Eyes’ (also with a green center, but having smaller flowers with yellow petals). The center does turn brown as the seeds develop.
The bright green leaves are 3-7” long and initially form a basal clump. Smaller leaves are produced on the flower stems. The strong stems and rough leaves are abundantly covered with short hairs (the species name hirta means hairy).
Like most Rudbeckias, ‘Prairie Sun’ grows best in full sun. It prefers moist, rich loam, but thrives in almost any soil and tolerates some drought once established. The plants thrive in hot and humid summers but also do well in cooler climates and stand up in heavy rains. These low-maintenance plants do not require staking. Space the plants at least a foot apart (up to 2 feet apart in warmer areas with a longer growing season) Deadhead spent flowers to encourage additional bloom but leave the flowerheads at the end of the season to reseed (or to be eaten by birds) and for winter interest.
Use groupings of ‘Prairie Sun’ in annual or perennial beds, in mixed borders or cottage gardens for a bold focal point, or intersperse them for more subdued impact. Individual plants can be used in large containers – alone or in combination with other complimentary plants, such as coleus and petunias. The bicolored petals blend well with both pastels and hot colors. It contrasts nicely with purple flowers or foliage, and pulls together orange and yellow flowers. The plants also fit well in meadows, looking stunning in late summer when planted in masses or drifts. Mix them with ornamental grasses such as feather reed grass (Calamagrostis ‘Karl Foerster’) or switch grass (Panicum ‘Heavy Metal’ and other cultivars), and blazing star (Liatris spp.) for a more informal, prairie-inspired planting that will be at its peak in late summer, or mix with the more airy Russian sage (Perovskia atriplicifolia) or blue mist spirea (Caryopteris) for a completely different look. They could even be set them out in rows to use just for cutting.
Although this cultivar is often billed as a perennial (zones 3-10), it is unpredictably short-lived, often acting as an annual or biennial, particularly in heavy soils. It grows quickly from seed and will bloom heavily in its first year, therefore it is best grown as an annual. This is a long day flowering species, so flowering and stem elongation is highly sensitive to daylength. When nights are longer than 12 hours (short days), seedlings produce a flattened rosette of leaves. But when there is more than 12 hours of light a day, leaf orientation changes to grow upwards, internodes elongate and plants initiate flowering. Seedlings of R. hirta can be started indoors in the spring with other bedding plants and transplanted outdoors. Some gardeners have success with winter sowing – planting the seed outdoors before the ground freezes. If started early, either direct-sown seeds (winter or spring) or those started indoors can flower the same season. Seedlings started later will only form rosettes and will flower the following summer if they overwinter. If not deadheaded, they may also self seed.
When sowing seed, barely cover as light encourages germination. Seeds should sprout in 10-21 days when held at room temperature (68-72˚F). Transplant into 3” pots when large enough to handle (if not sown in individual containers). Transplant into the garden after hardening off once all risk of frost is past. Protect the plants from rabbits (such as with fencing at least 2 feet high, or employ some cats for biological control). Slugs can also damage young plants. Fortunately, these are not favored by deer, though. Powdery mildew can be a problem but spacing the plants to provide air circulation will help prevent its development.
–Susan Mahr, University of Wisconsin – Madison