Use of Compact Fluorescent Lamps to Provide a Long-Day Photoperiod to Herbaceous Perennials

An experiment was conducted to assess the efficacy of compact fluorescent (FL) lamps alone or in combination with incandescent (INC) (INC+FL) lamps for providing low intensity long-day (LD) lighting to promote flowering of LD and inhibit flowering of short-day (SD) herbaceous perennials. The flowering responses of Campanula carpatica Jacq. (campanula) 'Deep Blue Clips' and Coreopsis grandiflora Hogg ex Sweet (coreopsis) 'Early Sunrise' (LD plants) and Chrysanthemum xmorifolium Ramat. (chrysanthemum) 'Auburn' and 'Bianca' (SD plants) were quantified. These perennials were grown in a greenhouse under a truncated 9-h photoperiod at 20 degrees C. Ten plants per treatment received a 6-h day extension (DE; to create a 15-h photoperiod) or 2- or 4-h night interruption (NI) by INC or FL lamps or 50% of each lamp type at a photosynthetic photon flux of 1.4 to 3.5 mu mol.m(-2).s(-1). An additional ten plants were grown as an SD control under a truncated 9-h photoperiod. LD plants did not flower under the SD photoperiod whereas 60 to 100% flowered under the LD treatments. Flowering time of LD plants was not influenced by the LD lighting regimen or lamp type. Under 6-h DE, coreopsis plants were 21% shorter under FL lamps compared with INC lamps. However, lamp type did not influence the height of coreopsis under 4- or 2-h NI or campanula under any LD regimen. Flowering of both chrysanthemum cultivars was inhibited or delayed by the LD treatments and lamp type did not influence the flowering percentage or timing. Under the LD treatments, flowering and non-flowering chrysanthemum 'Auburn' plants were shorter under FL lamps compared with INC lamps. Non-flowering 'Bianca' plants were shorter under FL lamps compared with INC lamps only under the DE treatment. Our results suggest that FL lamps can be successfully used to provide LD photoperiods to promote flowering of the LD perennials and inhibit flowering of the SD perennials tested in this study.