Pot culture of Black-eyed Susan (Rudbeckia)

To initiate flowering in Rudbeckia hirta, a day length of at least 14 hours is required; under insufficient light, the plant forms only a leaf rosette. At the same time, a day length exceeding 16 hours induces excessive stem elongation, which necessitates the use of plant growth regulators (PGRs) or the selection of genetically compact series with natural branching.

Pot culture requires the use of a well-drained substrate with the addition of 20–30% clay at a pH of 5.8–6.2. Plants require weekly nitrogen fertilization (150–225 ppm) and careful monitoring of the water balance: the high drying rate of the substrate necessitates regular irrigation, yet excessive moisture during cool periods encourages the development of root rots.

The production cycle from transplanting seedlings into pots of 11 cm or larger until the start of flowering takes 10 to 15 weeks. The fibrous root system of the crop requires sufficient container volume to prevent stress caused by the drying out of the root ball.