In the 1920s, W.W. Garner and H.A. Allard noticed that some varieties of soybeans planted at two-week intervals during May, June and July all flowered at the same time. After studying several variables, they discovered it was the length of daylight that influenced when these plants flowered. They coined the terms short-day and long-day plants. Since then, scientists have learned that it is the length of the night (darkness) that initiates flowering in certain plants. Long-day plants, plants that need short nights in order to produce flower buds, include fuschia, hibiscus, begonia, larkspur and delphinium.
Place your long-day plants near a south window for maximum natural lighting. Determine how many hours of natural light your long-day plants receive daily. Subtract that number from 16. This is how many additional hours of light you need to provide for the plants.
Install a fluorescent lamp above the area where you will set your plants. Put one cool and one warm white fluorescent bulb in the lamp. Position the long-day plants close to the light bulbs. Ohio State University Extension states that plants need to be 2 to 6 inches away from an artificial light source in order to obtain the appropriate intensity of light.
Supplement natural lighting by turning the lights on daily for the length of time needed, based on your calculations above. Maintain this routine for several weeks, until buds appear on your long-day plants.
Discontinue the supplemental lighting regimen after you notice flowering has been induced. Once plants have begun developing buds, they will flower at the same speed whether or not the days remain long.