The Effects of Different Colors of Light on Plant Growth
For my biology experiment, I chose to explore the process of photosynthesis. In photosynthesis, plants have pigments called chlorophylls that capture sunlight to synthesis oxygen and sugars such as glucose. Chlorophyll pigments are the primary pigment in plants and they absorb red and blue light the best. They reflect green light, which is why plants typically look green to us. I decided to test this with China Rose radishes.
My question that I am testing is what color of cellophane wrapped over the radishes, violet, red, or green, will make them grow the tallest? Based on this prior knowledge of colors of light and their effects on plant growth, I predict that the radishes planted under the violet and red cellophane will grow taller than the radishes under the green cellophane. I chose those three colors because violet and red are completely opposite on the electromagnetic spectrum. I think that this will be the outcome because the green cellophane should prevent the radishes from synthesizing sugars as well as the other colors, and therefore not grow as tall as the others.
Materials: The materials that I used were very simple to obtain. I visited the local Home Depot and Michael’s to buy all of the materials needed. The supplies I used are the following: * 3 sets of 8 connected peat pots. * 1 bag of Miracle Grow starter soil * 72 China Rose radish seeds * Well water * 1 red cellophane gift bag * 1 violet cellophane gift bag * 1 green cellophane gift bag * 1 pair of scissors * Three plastic forks * Camera * Measuring tape
Method: The independent variable is the color of light, being either violet, red, or green. The dependent variable is the height of the radish sprouts. Some controlled variables in my experiment are the type of plant I used, the amount of seeds I used for every color, the amount of sunlight they receive by placing them in the same location, the amount of water given to each subject, time when each subject was measured, and the amount of time they were left in the peat pots. I made sure to measure all three subjects at the same time of the same day of every week so that my data collection was correct and consistent. I also made sure to have a large sample size of 24 seeds for each color just in case some did not sprout correctly. I provided a much lower chance of error by using so many seeds for all three colors.
Procedure: After obtaining all of the needed materials listed above, I first started by putting an inch of soil in the bottom of every peat pot, which is a total of 24 peat pots, put into 3 separate groups of 8. I then put 3 radish seeds in each peat pot. After placing the radish seeds in there, I covered all of the seeds with another 2 inches of soil. The peat pots are 3 inches deep. I set the 3 groups of 8 peat pots on a table inside my outside covered greenhouse area. Setting the groups about 6 inches apart, I wrapped the bags of colored cellophane over the groups of planted radishes.
Every day, I went out at about 5 at night, uncovered the plants, and watered the plants with the well water that we use at our house. I put water into the peat pots until it overflowed out onto the table. After I was done watering them, I recovered them and put them back where they were. At week 3, they finally started to come out through the top and that is when I started measuring the growth of the leaves of each one. After the third week, I measured them every Thursday, and recorded the height of the plants until week 7. I used my phone camera and took the first set of pictures at week 6, when the radishes were able to stand up straight. At week 7, I could tell the radishes were starting to outgrow the little peat pots and my mom suggested it was time to transfer them into the ground in our yard. I dug 3 strips of dirt out about 6 inches apart from each other. The peat pots are made to be planted into the ground with the plants so I ripped the 8 connected parts for each color from each other, and planted them into the ground in rows with the different peat pots for each color about 3 inches away from each other in the row. I covered them with dirt until only the beginning of the radish root growing out of the peat pots was not submerged in the ground. Because the cellophane came in bags, I had to use scissors to cut them into long strips to cover the row of radishes. After cutting the cellophane into the right size, I watered the plants and then placed the strips of cellophane over the rows of planted radishes and used plastic forks to hold the cellophane into the ground. I did this to prevent the wind from blowing the cellophane away. On the Thursday of week 8, I took the last set of pictures and measured the plants for the last time.
Results: After measuring the radish leaves at week 3, the ones covered in red were on average ¾ of an inch in height. The tallest one was 1 inch in height, and the shortest was between ½ inch and ¾ inches in height. The ones covered in the green were slightly taller than the red ones. The radish leaves covered in green at week 3 were on average 1 ½ inches in height. The tallest one was 1 ¾ inches in height, and the shortest was 1 ¼ inches in height. The radishes covered in the violet were the tallest. On average, the height of the leaves were 2 inches tall. The tallest radish leaves covered in violet were 2 ½ inches tall, and the shortest was 1 ½ inches. At week 3, it looked as though the radishes in violet were growing the fastest. Every week after that, I measured them and the green and violet covered plants seemed to grow at almost the same exact rate, with the leaves getting about ½ an inch every week. The ones covered in red were the slowest growing. They only got about ¼ of an inch higher each week. By week 7 when it was time to plant them in the ground, I was very surprised to see that no actual radishes has sprouted. There were only leaves and the amount of time for this type of radish should only be about a month and a half. I continued to transfer them into the ground, thinking that would help. At the final time of measurement, week 8, there were still no actual radishes that I could see. The final height of the plants were not what I had expected either. The final average height of the leaves for the radishes covered in red was only 2 ¼ inches, the green was at 3 ¼ inches, and the violet was the highest at 4 ½ inches.

Table 1: Plant growth per week | WEEK 3 | WEEK 4 | WEEK 5 | WEEK 6 | WEEK 7 | WEEK 8 | VIOLET | 2 inches | 2 ½ inches | 3 inches | 3 ½ inches | 4 inches | 4 ½ inches | GREEN | 1 ½ inches | 2 inches | 2 ¼ inches | 2 ¾ inches | 3 inches | 3 ¼ inches | RED | ¾ inch | 1 inch | 1 ¼ inches | 1 ½ inches | 1 ¾ inches | 2 ¼ inches |

Conclusion: Previous to starting this experiment, I predicted that the red and violet covered plants would grow the most, leaving the green covered radishes being the shortest. No radishes actually sprouted by the end of my experiment, but the height of the leaves was not what I had predicted. I will have to reject my hypothesis. I am rejecting it because although the violet was the best growing, I predicted that red would also be bigger than the green, which it was not. The radishes covered in red were actually the least tall of all three. From the beginning, the red covered radishes did not do as well as the other two.
I think what my results mean is that radishes absorb more violet light than red or green. I am basing this conclusion on the fact that the radishes covered in the violet light grew taller than the red and the green. Some plants use different colors of light to grow, and I can only assume that violet is a very absorbable color for China Rose radishes. From doing this experiment, I learned that the chlorophyll pigments in radishes must be better at absorbing the violet end of the spectrum versus the red end of the spectrum.
Errors: The covered greenhouse at my mother’s house was placed in the spot so that it could obtain as much sunlight as possible, but maybe there was blockage from trees at some parts of the day. Another error that could have occurred is how far I planted them into the peat pots. If they were too far down, they may not have been able to soak up enough of the water and therefore never sprout into actual radishes. The amount of time for this type is at most 2 months, which is the amount of time I measured them for exactly. The red cellophane was the worst, which completely rejects my hypothesis. I predicted them to grow faster than the other radishes, and they did not do that. This could have been caused by lack of sunlight because the red ones were on the corner of the table. I watered the plants every day, but they may have had a lack of sunlight at times of the day where I was not able to be home to monitor the sunlight reaching them.
If I were to redo this experiment, I would not put them into the greenhouse first. I would immediately plant them into the ground and see if that changes the outcomes. I would also make sure to see the sunlight at different times of the day to ensure that they are getting enough sunlight to actually sprout. I might also get better quality soil to see if that changes it as well.

Sources: J. Stein Carter. Photosynthesis. Biology Education. Web. August 15, 2000. http://biology.clc.uc.edu/courses/bio104/photosyn.htm How do different color filters affect plant growth? UCSB Scienceline. Web. June, 2001.
http://scienceline.ucsb.edu/getkey.php?key=3155