From Seed to Seed:
Plant Science for K-8 Educators

Digging Deeper

Long-Day and Short-Day Plants

Every plant for which flower initiation is light dependent (and that is not the case for all plants) has a critical day length associated with it. The term long-day describes plants that begin forming flower buds when the days are longer than their critical day length. Two common long-day plants are dill and spinach. The term short-day, on the other hand, describes plants that begin flowering when

the days are shorter than their critical day length. Chrysanthemum and poinsettia are familiar short-day plants. Generally, long-day plants flower in the summer and short-day plants flower in the spring or fall. Day-neutral plants form flowers independent of day length. These plants, such as cucumber, tomato, pea, corn, sunflower, and dandelion, simply begin flowering once they have reached a certain age.

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