Provide pots that are 4 and 6 inches in height. Have your children plant two to five cactus seeds in the pot with soil. Usually cactus plants require potting soil that drains water easily so that they don't become over-hydrated. Look at the directions on your package of seeds before you purchase the soil. Instruct students to keep the soil moist, but not overly wet. Place the pots in a sunny area of the house or classroom. Check on the hydration levels of the soil each day and water as needed. Have the children record their progress and setbacks.
Have your children plant cactus plants that have already begun growing. Purchase cactus plants from your local greenhouse or retail outlet. Read the weather instructions on your cactus before the purchase. Provide the children with a sunny place outdoors to plant the cactus. Plant the cactus in the spring or summer months. Make sure you use soil that is well drained so the cacti aren't overly watered. Plant the cacti in a flowerbed and surround the plant with rocks and stones so that the plant has protection from the wind and rain. Have the children monitor the rain levels, growth process, and the frequency of watering that they need to do on their own.
Use a plastic wrap planting method. Have your children plant cactus seeds in easily draining soil in a flowerpot. Tell them to cover the flowerpot with plastic wrap and secure it with a string or rubber band. Cut a pen-sized hole in the plastic so that oxygen can get to the plant. Check the soil everyday for two to three weeks to make sure that it stays moist. As the plant begins to grow, slowly cut away the plastic day by day as you still want to keep some of the the plastic as it helps to hydrate the plant. Record the findings.
Require children to plant a series of cactus plants, one using each method. Have them record their findings individually and then require them to compare findings with each method. Ask them a series of questions, such as which plant thrived more. By using all three methods, you will teach them the value of comparing and contrasting experiments.