This activity helps students to gain a better understanding of the structure of a cactus. Ask your class if they know what a cactus is and if they can describe one. Show them pictures of various types of cacti and bring in real cactus plants, if possible. Give each child a lump of modeling clay or dough and instruct them to make a cactus shape out of it. You might want to assist your students if some have trouble with this. Discuss how cacti come in different shapes and sizes. Give each student a paper or foam cup and some sand. Have them set the clay cactus in the cup and sprinkle sand around it. Discuss how cacti grow in desert climates. Give each student some toothpicks (with blunt ends) and have them stick the toothpicks into the cactus. Talk about how the cactus' spines help to protect it. Display your children's creations or allow them to take them home.
This activity compares what a cactus needs versus what other plants need in terms of growth and health. Discuss with your students how cacti need much less water than other plants, which makes them more suited to desert climates. Buy a small potted cactus, along with several other small potted plants. You might use other plants such as a tomato plant and a miniature rose bush. Set the three plants in a well-lit area of the classroom. Tell your class that you are going to water the plants once every four days. Ask them to guess what might happen to the plants. Choose a student to water the plants on the fourth day. Continue this pattern every four days and discuss any changes that the students might observe. You might want to change your watering schedule to once a week if you aren't seeing much change at first. You can document the process with pictures of the plants every few days. After a few weeks to a month, compare the plants and discuss why they look differently. Talk about how many plants need frequent watering whereas cactus plants do not.
This science activity helps students to learn about which types of soil are best suited for cacti. Obtain three small cactus plants and plant one in sand, one in black dirt and one in soil that has a heavy clay content. Keep the cacti in the same area of the classroom and give them the same amount of water. Talk with your class about which type of soil they think will work best and why. Once a week, bring the cactus plants to everyone's attention and discuss any noticeable differences. You might even have your students draw how they think each cactus looks. After a set period of time (maybe three to six months), have your class vote on which plant they think looks healthiest. Discuss the desert climate that cacti are native to and the type of soil that is found there (sand).