Photoperiod can be an important environmental variable for dahlia seedling (plug) production. During a 7 week plug production scheme, long days provided by a 4-h night interruption with ≈10 fc of incandescent light inhibited tuberous root development while increasing shoot fresh and dry weight, fibrous root dry weight, leaf area, and height. Night interruption reduced plug production time by 1 to 2 weeks and plugs grown under long days showed superior growth following transplanting to 10-cm pots. No significant difference in total plant fresh and dry weight was observed between long-day and short-day plugs, indicating that growth differences were a result of photoperiod alterations in carbohydrate partitioning. Tuberous roots of short-day-grown plugs showed a 156% increase in fructan concentration (mg/g dry wt. basis) over long-day plugs. The carbohydrate status of long-day (night interruption) tuberous root tissue was characterized by high glucose concentration. The accumulation of glucose (a product of fructan synthesis), in plugs grown with night interruption is believed to be the result of slower rates of cell wall formation in long-day plugs compared to short-day plugs. HPAEC-PAD separation of fructans showed a maximum degree of polymerization of ≈30 in short-day tuberous roots and 27 for long-day tuberous roots. Effects of photoperiod on fructan metabolism in dahlia tuberous roots and the practical use of photoperiod in dahlia plug production are discussed.