So you're planning an experiment on how different liquids affect plant growth for this year's science fair. Even though you already have the general idea, you'll need to think through all of the details in order to give your science fair project the best chance. Make sure you focus on the different conditions of the experiment, as well as how you will display the information about your experiment, in order to make sure that the judges will take notice of your thought-out project.
Types of Liquids to Use
You can use several different groups of liquids in this type of experiment. The most basic (but least scientifically interesting) experiment would have you using random liquids from around the house, from orange juice and apple juice to liquid cleaner or even urine. Most would guess, however, that plain water would work better than any of these variations. Instead, consider trying out different types of water--distilled water, tap water, mineral water, and water from a nearby stream or swamp. You could also try out different liquid fertilizers to see which does the best job.
Ways to Measure Plant Growth
You may think that it is easy to measure plant growth--until you find that one of your plants has grown 3 inches fewer than the others but has dozens of flowers all over it. In order to take accurate data, you'll need to define your methods of measuring the flowers before you begin the experiment. You may want to rely solely on height, especially if you're trying to simplify the experiment. Alternately, you can create a chart with a column for each factor that measures plant growth: height, number of leaves, number of flowers, thickness of stem, or any other factors that may affect the specific plants you choose.
Type of Plants
Make sure to choose fast-growing plants for your science experiment--unless you plan on spending months taking data. Examples of fast-growing plants are marigolds, zinnias, sunflowers, radishes, beans, cucumbers and cress. Make sure to use seeds from the same package in your experiment so that the type of liquid is your only variable.
If possible, time your experiment so that you will be able to put your plants on display while they are still alive and thriving. You can place them in front of your display board, or off to the side of your display, if room allows. Make sure to take photographs of your plants at each stage of development, and attach one from each stage (clearly labeled) to the bottom center of your tri-fold board to show the plants' development. For an artistic touch, you can paint vines crawling up your display board in extremely light background colors before attaching your information to the board. Make sure that the background vines do not overwhelm the important information.