Cooling accelerates flowering of Lysimachia clethroides Duby

The effect of cooling method and duration on off-season cut flower producti on of Lysimachia clethroides Duby was examined. Rhizomes harvested in Octob er were cooled for 0, 4, 6, 8, 10, or 12 weeks at 4 +/- 1 degrees C in crat es with unmilled sphagnum peat moss or in 3.75-L, pots filled with a commer cial soilless medium prior to forcing in a warm greenhouse. After 6 or more weeks of cooling, shoots emerged from crates in higher percentages than fr om pots. However, only the duration of cooling, not the method, affected th e rate of shoot emergence, visible bud formation, and anthesis of the first bud in the raceme. As cooling increased from 0 to 12 weeks, the greenhouse days required for shoot emergence, visible bud formation, and anthesis dec reased linearly. The number of flowering flushes and flowering stems produc ed per plant varied quadratically with cooling duration, and the highest yi elds occurred when rhizomes received between 4 and 10 weeks of cooling. Hig h numbers of flowers were produced rapidly after 10 weeks of cooling. As th e number of successive flowering flushes increased, the stem length increas ed linearly while the stem diameter decreased linearly.