Rudbeckia hirta ‘Prairie Sun’

The genus Rudbeckia is a piece of America, although named after a Swedish botanist. The species hirta is native from Maine to Pennsylvania, west to the prairies of Illinois and south to Alabama and Georgia. Therefore, it is very appropriate for our group of specialty cut flowers growers to produce and sell this beautiful group of native plants. The German seed breeder Benary changed the landscape of available cultivars with the recent introduction of an entire rudbeckia assortment, ranging from the compact ‘Toto’ series to the tall ‘Prairie Sun’. Especially the award-winning ‘Prairie Sun’ received the attention of ASCFG members in the ASCFG Annual Seed Trial and deserves some space in the “New Varieties Issue”.
Rudbeckia hirta is an annual or biennial further south. It might survive the southern winters, but it should not be considered a true perennial.  ‘Prairie Sun’ has large, two-toned flowers from 6-8” (15-17 cm) with golden petals and light yellow tips. The contrast to the unusual green center makes this flower so attractive as a cut flower. Betsy and Alex Hitt in North Carolina liked this contrast especially for their late spring sales before customers are looking for typical summer colors. The stem length is 28-32” (70-80 cm).

You can purchase either seeds or plugs from your favorite seed or plug supplier. Seeds are sown for field production from early February to April for flowering naturally from mid-May through September. Southern growers in USDA hardiness Zone 8 reported direct transplanting into the field in October and in spring up to early May. Germination takes place at 68-72 F./20-22 C. in 8-14 days. In plug stage II, maintain this temperature and reduce humidity levels when propagating in the greenhouse. Begin feeding with 50 ppm nitrate nitrogen. In stages III-IV, the temperatures can be reduced gradually to 64-68  F./18-20  C. with fertilization up to 75 ppm N. Transplant after 3-4 weeks into the field or ground beds in hoop houses or greenhouses. Grow on at 60-64  F./15-18 C. Night temperatures should be maintained at 50-55  F./10-13 C. Fertilize weekly with 150 ppm nitrogen in a well-balanced formula.

‘Prairie Sun’ as a Cut Flower

The field spacing should be 8×10” /20-25 cm. Crop time from sowing to flowering in the north is approximately 17 weeks, in the south 16 weeks. Crop time from a 72-plug is approximately 12 weeks. The average yield is between 12-18 stems/plant. Harvest when the flowers are starting to open. Vase life is up to 25 days in floral preservative (hydration, holding solution). New research by Dr. John Dole and Frankie Fanelli at North Carolina State University presented at the ASCFG International Conference in Vancouver, BC and published in this issue show shelf life up to 21 days without any preservatives. Ethylene is not a significant factor with members of the Aster family.

Light Requirements

Rudbeckia is a long-day plant. It requires long days above 12 hours up to week 12 or the spring equinox. For field production in summer, this is not so relevant since most of the crops will be planted for flowering naturally from June-October. The southern fall plantings will overwinter as a rosette. Stem length will only increase and flowers initiate when the day length goes over 12 –14 hours. However, hoophouses have become more and more important to our growers to extend the season. Early spring crops can be produced under supplemental assimilation HID lighting to reduce crop time and achieve growth that is more vigorous. Increase your day length to 14-16 hours either by continuous lighting or night interruption. Greenhouse temperatures should not drop below 50-55  F./10-13 C.

Pests and Diseases
Important for Rudbeckia is to keep appropriate spacing, otherwise, plants succumb to botrytis. This can happen in the plug or transplanting stage already, but more importantly in regions with high heat and humidity in summer in the field. Good aeration will prevent this. Other fungal attacks can be caused by powdery mildew. Pests include thrips and aphids.
For color fact sheets with technical information, please contact our Sycamore office at (815) 895-6705 or [email protected] or