long-day plant A plant in which flowering is favoured by long days (i.e. days when there are more than 14 hours of daylight) and correspondingly short dark periods. There are two groups of such plants, species in which there is an absolute requirement for these conditions (such that flowering will not begin without them) and others in which flowering is merely hastened by them. Spinach, lettuce, and grasses are long-day plants; in Britain all of them flower in summer.

long-day plant A plant in which flowering can be induced or enhanced by long days, usually of more than 12 hours of daylight. Examples are spinach and spring barley. See photoperiodism. Compare day-neutral plant; short-day plant.

long-day plant A plant in which flowering is favoured by long days (i.e. days when there are more than 14 hours of daylight) and correspondingly short dark periods. There are 2 groups of such plants, species in which there is an absolute requirement for these conditions (such that flowering will not begin without them) and others in which flowering is merely hastened by them. Spinach, lettuce, and grasses are long-day plants; in Britain all of them flower in summer.