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Where and why do plants grow better, in the darkness or in the light?
Question Date: 2016-02-26
Answer 1:

The short answer is that plants grow better in the sunlight. This is similar to asking whether animals grow better with or without food. However, like with animals and food, the type and amount of light that plants need is important and may differ from plant to plant.

Plants use the sun's energy to break down carbon dioxide to form the cellulose that forms their leaves and stalks. With too little sunlight, plants have to rely on stored energy to live and grow. Thus, a healthy plant can survive short periods of darkness but will eventually wither and die without enough light. Too much sunlight is also a problem. Lots of sunlight usually means lots of heat, which can cause the plant to lose water and dry out. Intense light can also break down the colored compounds in the plant's leaves, causing damage. The color of the light is important too - plants can more easily use blue light than red light, and grow best when they can get the full spectrum of natural sunlight.

You can do your own experiments to test this, which would make a great science fair project.

First, choose the conditions you want to compare - for example, sunlight vs. shade or full spectrum vs. only red light. Then, buy a set of leafy houseplants from a nursery, choosing ones that are about the same size. (I recommend a variety of coleus, also called solenostemon.) Then, track the growth of each plant under the conditions you chose. Try to keep as many other conditions the same, like how often and how much you water them. Keep detailed notes on their height, how many leaves they have and what color they are. Taking pictures can help.

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