A student decides to set up an experiment to see if detergent affects the growth of seeds. He sets up 10 seed pots. Five of the seed pots will receive a small amount of detergent in the soil and will be placed in the sun. The other five seed pots will not receive detergent and will be placed in the shade. All 10 seed pots will receive the same amount of water, the same number of seeds, and the same type of seeds. He grows the seeds for two months and charts the growth every two days. What is wrong with his experiment?