Bulking Duration Affects Growth and Flowering of Herbaceous Perennials Grown Under Nursery Conditions and Forced Into Flower Under Night-Interrupted Lighting Outdoors in the Southern United States
The effects of bulking duration on growth and flowering of ‘Goldsturm’ black-eyed Susan (Rudbeckia fulgida Ait. ‘Goldsturm’) and ‘Moonbeam’ coreopsis (Coreopsis verticillata L. ‘Moonbeam’) forced into flower under nursery conditions were evaluated as part of a system for the accelerated production of herbaceous perennials requiring long days to flower. Bulking duration treatments were established by a factorialization of potting date (September 24, October 13, December 2, and December 14, 2009) and night-interrupted lighting (NIL) start date (February 1, February 22, and March 15, 2010). Leaf counts of black-eyed Susan at the beginning of NIL increased linearly with progressively longer bulking durations based on potting date and NIL start date, although the effect was more pronounced when compared across potting dates. Based on leaf counts, black-eyed Susan potted in December were still in the juvenile phase when NIL was begun on February 1, 2010. Stem counts of black-eyed Susan at first flower followed a similar pattern as leaf counts. Black-eyed Susan given NIL flowered 40 to 59 days before plants under natural photoperiod (NP). Flower plus flower bud counts of black-eyed Susan at first flower increased linearly with increasing bulking duration based on potting date: by 325, 268, and 243% when NIL was begun on February 1, February 22, and March 15, respectively. Flower counts also increased linearly approximately 46% with increasing bulking duration based on NIL start dates, but only when plants were potted in December. At first flower, plant height of black-eyed Susan given NIL increased linearly as bulking duration increased based on potting date, but did not differ when trended across the NIL start dates. Days to flower of coreopsis decreased with increasing bulking duration, while stem counts increased with bulking duration, and the number of marketable plants was greater when plants were repotted on the three earliest dates compared to those bulked the shortest duration. Effects of bulking duration on flower plus flower bud counts and height of coreopsis were inconsistent.