Short or Long Day Plants = Photosperiodism

Summary: The day length plays a part in plants flowering and fall into various groups depending on the day length, or photoperiod needed for flowering. Do you know if tuberous begonias are short or long day plants?

Question: What do they mean when people talk of short day plants and long day plants? Are they some special kind of plant? Pricilla, Red Bank, NJ

Answer: Pricilla, in the 1920’s, two government scientists, W. W. Garner and H. A. Allard, discovered while working with tobacco plants that day length had much to do with flowering response. They found plants fell into various groups according to day length, or the photoperiod required for flowering.

Chrysanthemum, poinsettia, gardenia, and many others initiate their buds when days are relatively short, while calceolaria, tuberous-rooted begonia, and many common annuals respond better to a long day. A third group, including the rose, African violet, and tomato, flowers regardless of day length.

tuberour red begonia flowering

Plant phenomena other than flowering can also be attributed to photoperiod. Some of these are runner production in strawberry (long day), bulbing in onion (long day), tuber formation in tuberous-rooted begonia (short day). Height, or internode length, of many plants is limited or extended by varying day length.

Discovery that plants can grow and flower under artificial light has given indoor gardeners a second field of horticulture. It is not a new field, however, for in the early 1880’s, exploratory work was tried out, although limited by lack of proper instruments.

In 1893, Liberty Hyde Bailey used are lamps to test some of his theories on the effect of ultraviolet rays on plants. Since then, work with artificial light in relation to plant growth has steadily progressed where today we find LED lighting used for growing indoors.

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