A study was conducted to determine the effects of night-interrupted (NI) lighting initiated at different times in late winter on several herbaceous perennials produced outdoors in a southern nursery setting. Treatments were NI lighting beginning February 1, February 15, March 1, March 15, and a natural photoperiod. NI lighting accelerated flowering in ‘Goldsturm’ coneflower (Rudbeckia fulgida Ait. ‘Goldsturm’) 26–46 days in 1999 and 51–75 days in 2000, and in ‘Coronation Gold’ yarrow (Achillea x ‘Coronation Gold’) 2–9 days in 1999 and 2–11 days in 2000. Flower and flower bud counts increased 82–100% in ‘Coronation Gold’ achillea in 1999, 44–51% in ‘Butterfly Blue’ scabious (Scabiosa columbaria L. ‘Butterfly Blue’) and 100–151% in ‘Alaska’ shasta daisy (Leucanthemum x superbum Bergmans ex. J. Ingram ‘Alaska’) compared to counts of plants under natural photoperiod. With few exceptions, plant height increased under all NI lighting treatments, but in only ‘Goldsturm’ coneflower did it reduce plant quality. Clump verbena (Verbena canadensis L.) was minimally affected by NI lighting, and speedwell (Veronica spicata L. ‘Sunny Border Blue’) was not affected at all.
4Associate Superintendent, Ornamental Horticulture Substation, Mobile, AL.