The effects of temperature and lighting on flowering of lavender (Lavandula angustifolia ‘Hidcote’)

Abstract

SummaryA series of three experiments was conducted to determine the effects of temperature and lighting on bud initiation and flower expression in lavender. A period of nine weeks at 4°C was shown to satisfy the vernalization requirement for all plants, and after five weeks at 4°C, 50% of plants flowered. Vernalization was shown to occur more slowly at temperatures above 4°C and was observed up to 16°C. Following vernalization, a higher temperature advanced bud appearance, with an optimum temperature of 20°C, but reduced the number of buds. When vernalization was incomplete, a higher temperature delayed bud appearance and reduced the number of buds. A daylength of 15 h compared with 8 h either during or after cold treatment increased the number of buds produced, suggesting that additional lighting may be needed for the winter production of plants in flower. Whilst it was possible to model flower development after bud appearance, unexplained variation between experiments in the time to first visible bud prevented satisfactory mathematical description of floral bud production. It was concluded that the “environmental history” of commercially micro-propagated material had a significant effect on the duration of cold required for vernalization, and that differences in the vernalization requirement of individual meristems led to variation in the cold requirements of plants within a crop. The commercial significance of these conclusions is discussed.