Night interruption lighting is beneficial in the production of plugs of dahlia 'Sunny Rose'

Experiments were conducted to evaluate effects of photoperiod on growth and dry-weight partitioning in Dahlia sp. 'Sunny Rose' during both seedling (p lug) production and subsequent production in 10-cm pots. Plugs were grown u nder short days [9-hour natural photosynthetic photon flux (PPF)] or long d ays (same 9-hour PPF plus a 4-hour night interruption with incandescent lig ht). Total plant dry weight was unaffected by photoperiod; however, long da ys (LD) inhibited tuberous root development and increased shoot dry weight, fibrous root dry weight, leaf area, shoot length, and number of leaf pairs . Long days reduced plug production time by approximate to1 week compared w ith short days (SD). Following transplanting to 10-cm pots, shoot growth an d foliar development were superior under LD. There was no effect of photope riod on foliar N concentration. The superior growth of LD plugs following t ransplanting can be attributed to the plant being in a physiological state conducive to shoot expansion instead of storage.