Do you think plants need dirt to grow? How could you find out?
What do you think will happen?
Compare these two tomato plants. The one on the left grew in dirt. The one on the right grew in water, but no dirt.
Discuss: Which plant looks healthier? Why?
Our experiments show that plants need water and dirt to be healthy. What else do they need?
Which plant do you think is healthier: the one that grew in the light or the one that grew in the dark?
Why do you think that?
For this experiment, you need food coloring, vases or cups, and white flowers. (Carnations work well.)
Add food coloring to water, then put the flowers in the colored water and wait. Depending on the type of flower and the humidity, it may take a few hours or a day to see results. (For detailed instructions and an explanation, check out Fun Learning for Kids.
Discuss: What do you think will happen?
When you see results, discuss: Why do you think that happened?
If the demonstration of water traveling into a flower intrigues your students, you can give them a chance to examine this more closely.
Cut some pale lettuce leaves from a lettuce head and put the cut end in red or blue-colored water. (Butter lettuce works well.) Like the flower, the lettuce leaves will soak up the colored water, revealing a pattern of veins in the lettuce leaf. Have children draw the pattern of veins in a lettuce leaf. These are usually difficult to see, but the food coloring makes them visible.
You can do other experiments involving dyes in leaf veins.
If your students are interested in growing plants in water (without dirt), try making a very simple hydroponic garden. All you need is a damp kitchen sponge or piece of cotton cloth, sprinkled with lettuce or radish seeds.
Your students can write their names in seeds, and watch them grow, following the very simple instructions from Tim Hunkin.