Use of Compact Fluorescent Lamps to Provide a Long-Day Photoperiod to Petunia and Pansy

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 herbaceous LD plants. The LD plants Petunia ×hybrida Vilm.-Andr. (petunia) ‘Single Dreams Red’ and ‘Purple Wave’ and Viola ×wittrockiana Gams. (pansy) ‘Colossus Yellow’ and ‘Delta Blue Blotch’ were grown in a greenhouse at 20 °C. Plants were grown under a truncated 9-h photoperiod with or without a 6-h day extension (DE; to create a 15-h photoperiod) or a 2- or 4-h night interruption (NI). The DE and NI treatments were provided by INC and FL lamps, alone or combined, at a photosynthetic photon flux of 1.4 to 3.5 μmol·m⁻²·s⁻¹. Petunia ‘Wave Purple’ did not flower under the SD photoperiod whereas 60% to 100% flowered under the LD treatments at 10 weeks after transplant. Time to flower was most rapid under the INC or INC+FL lighting treatments. In addition, plants under DE and 4-h NI generally flowered earlier than under the 2-h NI. All petunia ‘Single Dreams Red’ plants flowered within 65 days after transplant, although flowering occurred earliest under the DE and 4h-NI when provided by the INC or INC+FL lamps. In addition, INC lighting promoted stem elongation of both petunia cultivars. In pansy, all LD treatments promoted flowering of ‘Colossus Yellow’ compared to plants under short days; ‘Delta Blue Blotch’ was less responsive to photoperiod.  Collectively, our results indicate that flowering of some LD plants is delayed when FL lamps are used alone to create an artificial LD.