PHOTOPERIOD RESPONSES OF TEN SPECIALTY CUT FLOWERS

Nine cut flower species and cultivars, Ageratum houstonianum Mill. ‘Tall Blue Horizon’, Antirrhinum majus L. ‘Spring Giants Mix’, Carthamus tinctorius L. ‘Lasting Yellow’, Celosia argentea L. ‘Chief Mix’, Cosmos bipinnatus Cav. ‘Early Wonder’, Helianthus annuus L. ‘Sunbright’ and ‘Sunrich Orange’, Tagetes erecta L. ‘Promise Orange’ and Zinnia violacea Cav. ‘Benary Giant Deep Red’ were grown under 8, 12 or 16-h photoperiods. Ageratum, Antirrhinum, Carthamus and Tagetes were determined to be facultative long day plants and Celosia, Cosmos, Helianthus (both cultivars) and Zinnia were facultative short day plants. Antirrhinum and Tagetes stems produced under all three photoperiods were large enough to meet minimum harvest length (45 cm). Ageratum plants should be grown under 8-h photoperiods to produce stems long enough to market before subjecting the plants to inductive 12 or 16-h photoperiods. Carthamus plants should be grown under either 8 or 12-h photoperiods before providing inductive 16-h photoperiods. Celosia and Cosmos should be grown under 16-h photoperiods before providing inductive 8 or 12 h photoperiods. Helianthus and Zinnia plants should be grown under 16-h photoperiods before providing inductive 8 or 12 h photoperiods.