In order to test the way caffeine affects plant growth, you need four plants of identical size and species. One plant will subsist on nothing but regular water. In science terms, the plant that receives only water is the "control." The control is what you compare your findings against to see whether the other test subjects have significant differences from the control subject. The three remaining plants will all receive different amounts of caffeine to determine whether increased caffeine consumption affects their growth. Give the plants the same amount of water sunlight each day. Record your findings to determine whether the caffeinated plants have increased or decreased growth.
Testing how plants react to music is an enjoyable project that allows you to listen to some of your favorite music while you work. Choose three different music genres and use four different plants. Expose three of the plants to a different genre of music. Leave one plant to grow without music at all. Give the plants a consistent amount of sunlight and water each day. Record the different growth rates of each plant to see which genre works best at influencing the plants' growth.
There are many different factors in your town that can affect the fertility of your soil. Attain a map of your town and break it into quadrants or smaller regions if necessary. Collect soil samples from each region on the map and label it. Place the soil from each site into its own pot and attempt to grow plants in the different pots. It is imperative that you provide each seed with the same amount of sunlight and water to obtain accurate results. Mark the most fertile locations on the map.
There are many different fertilizers you can choose from to give your plant the best chance at life. Some fertilizers use organic ingredients whereas others have synthetic growth hormones developed in labs. Provide two test plants with an organic fertilizer and two test plants with a synthetic fertilizer. Monitor their growth to determine whether the organic or synthetic fertilizer works best for growing a healthy plant. Test more than one type of each fertilizer to obtain consistent results.