How to Care for an Old Man Cactus. The old man cactus takes its name from the long, white hair-like strands which grow out of the spiked column that makes up the plant. Like most cacti, the old man cactus is easy to care for. Follow this guide.
Give an old man cactus as much light as you can provide in your home. The plant tolerates any amount of sunlight and more is better. The more light the plant receives, the longer and thicker its hairs will grow.
Encourage an old man cactus to have a dormant period in the winter. Because it receives less light in the winter, winter growth is likely to be weak and undesirable. However, by placing in a cool environment, the plant will not grow in the winter. Temperatures between 50 to 65 degrees Fahrenheit are best.
Water the cactus several days after the soil has finished drying out. An old man cactus is more likely to be damaged from over-watering than under-watering, so it's important not to water it unless the soil is dry. However, when the soil does dry out, give the plant water until it runs out of the drainage hole. Giving the plant less water than usual in the winter also encourages the plant to go dormant.
Repot into the next size pot when roots wrap around the bottom of the pot. Because the old man cactus is slow growing, this may take several years. When repotting, fill the pot with a potting mix made especially for cacti. As an alternative, add one part course sand to two parts regular potting mix.
Care for the hairs of the old man as they become brown and dirty by cleaning them with a solution of water and detergent. Mix the solution, apply with a brush and then rinse the plant with plain water. Cover the potting mix with a sheet of plastic so the detergent does not seep into the soil. Or, simply accept that your old man cactus is beginning to look more like a young man.