Sunflower (Helianthus annuus), an annual native to North America easily recognized by its large yellow flower-head that resembles the sun, cannot survive without light. Like any plant, it has a unique relationship with light that allows for the production of energy required for life. The plant can, however, live without sunlight.
Photosynthesis is the process used by plants to convert the energy that comes from light into chemical energy they can use for food. The process takes place in the sunflower's leaves, which are heart-shaped and grow up to an inch in length. Photosynthesis depends on water, gathered by the plant's roots; carbon dioxide, gathered from the air; and light, which is gathered by chlorophyll, the green pigments in the leaves. Light gathered by the chlorophyll is split into molecules of hydrogen and oxygen, using water. The hydrogen then joins with carbon dioxide to produce food for the sunflower.
Sunflowers Can Grow Under Artificial Light
The light needed for sunflowers to live does not have to come from the sun. Sunflowers are successfully grown indoors under artificial light. As early as 1952, sunflowers were being grown from seed under warm white fluorescent lamps supplemented with incandescent bulbs in studies. In one study, they were grown alongside peas and tomatoes to measure the plants' reaction to light and dark cycles. Sunflowers are often used in science-fair projects due to their ability to thrive under artificial light.
In the garden, sunflowers require full sunlight to grow. They do not tolerate shade. When grown indoors under artificial light, sunflower seedlings require 18 to 20 hours of light a day to grow. The seedlings should be placed 4 to 6 inches below fluorescent tubes. The amount of light can be reduced to 16 hours a day, to encourage the plants to flower once they reach a height of 10 to 12 inches.
Sunflowers grown in natural light are said to follow the sun, due to a process known as "phototropism." As the sun moves overhead throughout the day, the flower-head of the sunflower "tracks" it, turning to face the direction of the sun. The process cannot occur in the absence of light, but since it is induced by light stimulus, sunflowers grown under an artificial light source will react to light in the same manner.
- University of Cincinnati; Photosynthesis
- National Center for Biotechnology Information; Possible Interactions Between Light-Dark Cycles; Harry R. Highkin et al; 1952
- University of Southern California; California State Science Fair 2005 Project Summary
- Cornell University Extension: Indoor Gardening Under Lights
- Bioweb: Helinathus Annuus-Lifestyle Variations
- University of Hamburg; Botany Online: Growth Movements -- Phototropism
- Photo Credit Jupiterimages/Photos.com/Getty Images
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