How to Care for a Small Dying Cactus

Dip a knife into a sterilizing mixture of 70 percent denatured alcohol and 30 percent water. Cut off areas of the cactus plant that look slimy, discolored or show symptoms of rot. Make cuts into the healthy areas of the plant.

Shake fungicide powder that contains sulfur on rotted areas of the cactus. Lift the cactus out of its container. Pour out the soil and replace it with clean cactus potting medium. Generally, cactus potting soil is made up of 60 percent pumice, 20 percent coir and 20 percent topsoil. Place the cactus in the new potting soil.

Dilute insecticidal soap with water. Spray cactus plants that are infested with aphids, mealybugs or scales. Keep the cactus watered. Cactus plants become damaged by insecticidal soap when they are water-stressed. To know when to water a cactus, feel the soil. It must be completely dry before water is added.

Place the cactus near a south-facing window. A small cactus should not receive direct sunlight. Hang a sheer curtain over the window if the cactus discolors or burns.

Fertilize your small cactus plant in the spring, summer and fall. Use a fertilizer that has an NPK amount of 5-10-5. Dilute the fertilizer in water, according to the directions. Pour the mixture into the pot until it runs out of the drainage hole.