This is how the length of the night affects the blooming of your plants

Poinsettias are Christmas flowers because they naturally flower in December when the night is longer than the day. (Suju Foto/Pixabay)


The flowering of the crops is affected by several factors, one of which is light duration, more specifically, the length of a night. You may notice that some flowering ornamental crops only flower during a particular season of the year.  Some crops need specific night lengths for them to flower, while others may be unaffected. The response of plants to initiate flowering depending on the duration of night is called photoperiodism. The photoperiod behavior of plants may be categorized as short-day, long-day, or day-neutral.

Poinsettias are Christmas flowers because they naturally flower in December when the night is longer than the day. (Suju Foto/Pixabay)

Short-day plants

Short-day plants bloom when nights become longer. They form flowers only when the day length is less than 12 hours. In the Philippines, short-day periods occur from September to February. Short-day plants include chrysanthemums, dahlias, and poinsettias. Not only ornamental crops, but also some vegetables like soybeans, winged beans, hyacinth beans, and pigeon peas tend to flower more during this season.

Long-day plants

Long-day plants, in contrast, require short nights to flower. They bloom when they are exposed to more than 12 hours of light. These plants include asters, coneflowers, petunias, snapdragons, daisies, and sunflowers. Long days happen in the months of March until August.

Day-neutral plants

Day-neutral plants form flowers regardless of day length, so they can naturally bloom throughout the year. Petunias, begonias, geraniums, marigolds, roses, African violet, tomato, corn, and cucumber are some examples of day-neutral plants.

Chrysanthemum flowers can be produced off-season by covering the plants for at least 12 hours to simulate a short-day period. (Didgeman/Pixabay)

Practical implications

Determining the photoperiod behavior of plants may help gardeners plan when to expect their crops to flower. For commercial purposes, the day length and night length can be manipulated to force the flowering of plants outside their natural blooming season. For example, chrysanthemums and poinsettia can be covered for more than 12 hours for several weeks to make them bloom during the summer season. On the other hand, long-day plants can be exposed to artificial grow lights to simulate longer daylight for them to bloom during the short-day season.

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