Phlox paniculata L., or garden phlox, is an herbaceous perennial in the family Polemoniaceae native to the eastern United States. Flowering stems of phlox are a popular item in cut flower markets because of their wide range of flower colors, large inflorescences, and pleasing fragrance (Armitage and Laushman, 2003). Plants may reach a height of 1.5 m, under favorable conditions, and the 2.5-cm diameter, tubular flowers are borne in dense, terminal cymes up to 20 cm across (Griffiths, 1994). It is a quantitative long-day plant with a critical photoperiod of ≈13 h. (Runkle et al., 1998); however, natural flowering occurs in mid- to late summer, well beyond the peak demand period for cut flowers.
Off-season greenhouse forcing of P. paniculata can allow growers to produce flowering stems during the most favorable marketing periods, and previous studies with P. paniculata showed that long-day photoperiods could induce flowering and cold treatment can accelerate flower development and increase length of the flowering stems (Iversen, 1989; Iversen and Weiler, 1994). The objective of these investigations was to determine the influence of cooling on the number of greenhouse days to flower, flowering stem length, and yield of cut flower stems of P. paniculata forced under incandescent and high-intensity discharge lighting.
Armitage, A.M. & Garner, J.M. 1999 Photoperiod and cooling duration influence growth and flowering of six herbaceous perennials J. Hort. Sci. Biotechnol. 74 170 174
Garner, J.M. & Armitage, A.M. 1998 Influence of cooling and photoperiod on growth and flowering of Aqueligia L. cultivars Scientia Hort. 75 83 90
Lewis, P.M., Armitage, A.M. & Garner, J.M. 2000 Photoperiod affects growth and flowering of Lysimachia clethroides Duby HortScience 35 596 599
Runkle, E.S., Heins, R.D., Cameron, A.C. & Carlson, W.H. 1998 Flowering of Phlox paniculata is influenced by photoperiod and cold treatment HortScience 33 1172 1174