Lisianthus (or Eustoma grandiflorum) is a very popular cut flower in the UK.
Although most cultivars flower earlier in "long days", the way the long day is produced has considerable influence. In the research discussed here, young Lisianthus plants were given a five-hour break nightly, using one of four light sources.
Three were fluorescent lamps ("far-red", "plant-growth" and "daylight-type"), while the fourth was an incandescent lamp. As the names imply, one lamp emitted most of its energy in the far-red while the daylight-type emitted more in the red waveband than the far-red. Control plants received natural autumn day-lengths.
The first plants to form flower buds were those under the "far-red" fluorescent lamp, and they also had the fastest rate of stem growth. Those under the incandescent and plant-growth lamps were next to bud while the untreated controls produced flower buds much later. Those under the "daylight-type" fluorescent lamp were the slowest to bud. None of the treatments affected the time taken for flower buds to develop into open flowers.
It is suggested that night breaks from either far-red fluorescent or incandescent lamps should be used when rapid flowering with long stems is required while the use of "daylight-type" fluorescent lamps would delay flowering.
Night-break Treatment Using Different Light Sources Promotes or Delays Growth and Flowering of Eustoma Grandiflorum (Raf.) Shinn. by Yamada, Tanigawa, Suyama, Matsuno and Kunitake (2008). Journal of the Japanese Society for Horticultural Science. 77 (1): 69-74.Available online at www.jstage.jst.go.jp/browse/jjshsh1.