Flowers soak up water from the ground through veins in their roots and stems. Since water is normally colorless, this process is hard to observe. If you color the water with food coloring, however, a white flower such a a carnation will start to show tinges of the added color. An easy way to demonstrate this to your class is to leave a cut flower in a vase of colored water overnight, or first thing in the morning. Check it periodically for signs of color. The longer you leave the flower in the colored water, the more intense the petal transformation will be.
For a variation, split the stem of a flower and straddle it over the rims of two adjacent vases. Add a different color to each vase and watch the flower develop two colors, one on each side.
Flowers don't like to be overcrowded any more than humans do. They depend on the wind to spread their seeds over a wide area so that they don't have to compete too fiercely for the light, soil and water resources available in a given patch of dirt. Demonstrate seed dispersal by testing how far different flower seeds will travel with different windspeeds.
Drop a few seeds of several different varieties in front of a blowing fan. Measure the time aloft and distance traveled. Try comparing results with different fan speeds to test the effect of wind speed on seed dispersal. Calculate the average distance traveled for each seed type and write a paragraph explaining how effective wind is as a method of ensuring the continuation of each species. Ask students to consider what other methods flowers might use to spread their seed around besides wind.
Flower gardeners hope for lush, colorful and abundant blooms to adorn their gardens and bouquets. To this end, they need to know which kind of plant food will produce the healthiest and prettiest flowers. Set up several containers of flowers to compare the effects of different types of plant food. Add a different nutrient to each container, such as a commercial plant fertilizer, sugar, plain water, baking soda, alcohol, aspirin and tea or coffee. Take pictures and notes over several weeks, looking for signs of health and vitality such as stem strength, leaf size, and overall plant health. Ask children to write a paragraph describing which plant food results in the healthiest flowers.
Flowers need soil, water, light and air to thrive. Children can experiment with removing one or more of the necessary nutrients, then compare the resulting growth rates. For example, plant one set of flowering plants in soil and set it in a sunny, airy location but don't water it; or plant another in gravel and give it light and water but no soil; or give another soil, water and air but put it in a dark closet with no light. Compare the health of the plants under each set of growing conditions.