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Name: Nicholas R.
Status: student
Age: 10
Location: N/A
Country: N/A
Date: 12/10/2002

I am doing a science project on "do plants need darkness to grow?" I know they need light, but do not know if they need darkness. I bought two plans and have one getting natural sunlight and darkness and the other one is under a light the entire time, but they are doing the same so I am not finding the answer this way.

I checked with a person at the local plant nursery and they described to me plants that can be in more darkness and plants that definitely need more light, but that does not answer my basic question. Any info would be appreciated!

It seems that the plant that you chose as a test plant gets enough light from the "artificial" light to meet its need for light in order to grow. Your experiment is a good one, but you might consider setting it up a little differently. Plant your seeds (two or three seeds to a pot, in case one is a "dud" and does not germinate). Do the same thing for one, two, or however many plant samples you want to use. Now leave pot #1 open to sunlight. Keep pot #2 covered except for, say about 1/2 hour each day (at the same time of day). Keep pot #3 covered except for, say about 3 hours each day (at the same time of day). Keep pot #4 covered all the time. Give each plant the same amount of water. Also, you can use as many pots and change the length of time you give the seedlings depending upon how much detail you want, and space you have.

Vince Calder

It would seem that your experiment IS telling you the answer to your question. If the plant without darkness is doing the same as the one with both light and darkness, then that species of plant, at least, does not need darkness.

Now, to answer your question fully, you would need to follow the plants throughout their life cycle. Will both plants have the same shape leaves, will both have healthy flowers, and make fertile seeds? Just watching the plants grow from seed for a few weeks will not tell you that.

Richard E. Barrans Jr., Ph.D.
PG Research Foundation, Darien, Illinois

Well, it really depends on the type of plant you have. If you think about it, different plants grow at different times of the year, when there is more or less sunlight. I think you know that plants need some sun for photosynthesis, but you ask a good question about whether they need any darkness. Are you plants the same kind? Are you treating them both exactly the same, so that the only difference between them is the amount of light? Perhaps your type of plant will grow in full sun or part sun. Have you tried different types of plants? One thing that might be affected that you have not seen yet is its ability to flower, or when it flowers. That might be different. Do not just look at the height, also look at the size of the leaves, how many flowers and seeds it produces, how green they are compared to the other, etc.

Van Hoeck

The following should be helpful

Most plants (C3) require time for respiration during dark hours. Some plants (CAM, e.g., cactus) actually carry on photosynthesis during the night to prevent water loss.

Anthony Brach, Ph.D

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