Photoperiod and irradiance effects on Salvia elegans, S. greggii, and S. patens flowering, height and brancing

Salvia is a large genus in the mint family (Labiatae). Some species (i.e. S. splendens and S. farinacea) are well known ornamentals; others, such as S. elegans, S. greggii and S. patens are not yet commercially utilized, in part, because of the difficulty in inducing plants to flower at desired times. Day length and light intensity are environmental factors involved in flower induction, and their effect on Salvia flowering was studied in this experience. Initially (Phase I), plants of S. elegans, S. greggii and S. patens were grown under one of the following lighting treatments: 1) short day (SD: 8-h photoperiod 0830-1630 HR); 2) night interruption (NI: from 2200-0200 HR with incandescent lamps [2 μmol m-2 s-1]); 3) day extension with additional 50 μmol m-2 s-1 (DE50; 0800-0200 HR with high pressure sodium lamps) or 4) day extension with additional 100 μmol m-2 s-1 (DE100; 0800-0200 HR with high pressure sodium lamps). Treatments 2, 3 and 4 are considered LD photoperiod treatments. After two weeks, plants were rotated among lighting treatments and remained under those conditions until flowering (Phase II). S. elegans was identified as an obligate SD plant: two weeks of SD were sufficient to induce flowering, but better overall plant quality was obtained when SD was maintained until flowering. S. greggii was classified as a facultative SD plant. S. patens flowering response to photoperiod was more complex; it required LD followed by SD for successful flowering. No species responds to irradiance with respect to flower induction, i.e. increased irradiance did not reduce node number below the first inflorescence. Effects of lighting treatments on plant height at flowering were also studied.