Make sure that every child understands what a hypothesis is and can write it in their journal. They should be able to answer this question: What will happen when you add white flowers to colored water? Ask every child in your classroom to bring in a white flower and put them together in a clear vase to make a bouquet. To determine what color of food coloring to use, take a vote among your students and keep a tally on the board.
Add about a teaspoon or two of food coloring to an average size vase three quarters full of water. Remember that you can mix two colors like red and blue to make purple. Add the flowers to the water in the vase. You can also divide the flowers into more than one vase and use different colors in each vase. This experiment can last up to five days, so be sure the students take notes in their journal every day.
Each child should compare their written prediction to the result. Explain that when you put a flower in water it soaks the water from the stalk of the flower all the way up the stem and nourishes the flower petals. You can make a graph on the board showing the days at the peak of color. Ask each child to make two graphs in their journal: one of their prediction, and one of the outcome; then compare the graphs.
Let the flowers sit on your desk or off to the side for the week and record how much the color changes and how long before the petals stop changing colors. Conduct a classroom discussion and ask the students to share their results. Take the discussion further by asking what would happen if you put colored flowers in clear tap water--would the flowers turn white again?