In general, petting cacti isn't recommended, but when you see one covered in soft, fine-spun hairs, it's hard to resist. Called alternately bunny cactus, white Persian cat cactus or most commonly old man cactus (Cephalocereus senilis), this is one that gets attention. Don't be fooled by the soft-looking cover though -- under the fine hair, this cactus has sharp yellow thorns. Old man cactus grows in U.S. Department of Agriculture plant hardiness zones 9b through 11.
1. Slow Growing Giant
With enough time, the old man cactus will grow 45 feet tall, but you don't need to worry about it taking over the house or garden. It takes years for this cactus to grow that tall, and if you keep it in a container indoors, it will stay small indefinitely. This erect cylindrical cactus has fine silvery hairs that wrap around it, covering sharp thorns.
2. The Illusive Flower
Unless you live in the desert and you can grow your cactus outdoors, it's unlikely to flower. Even in ideal growing conditions outside, old man cactus won't flower until it grows about 15 feet tall. When this cactus does finally flower, it opens at night in the spring. It's worth waiting up to see -- the 2-inch diameter pink flowers grow out of the soft white hairs.
3. Indoor Growing
If you don't want to spend a lot of time fussing with your houseplants, cacti are the way to go. Drainage is critical, but they can tolerate some neglect. When you plan, make sure the container has drainage holes in the bottom and use potting soil specifically for cacti and succulent s. Fertilize once or twice a month from spring through early fall using 1/8 teaspoon of 12-4-8 liquid fertilizer diluted in four cups of water. Allow the top 1 inch of potting soil to dry out between waterings.
4. Outdoor Growing
Warm climate desert gardening has its advantages, and one of those is that you can grow an old man cactus outside. Native to Mexico, this cactus can survive a light freeze and will grow in areas where winter temperatures drop to 25 or 30 degrees Fahrenheit. Plant it in full sun and rocky or sandy soil with good drainage. If you live in an area that gets between 12 and 14 inches of rain a year, you don't need additional water. Fertilize once in spring using 1/3 cup of 12-4-8 liquid fertilizer diluted in two gallons of water. Water the cactus when you fertilize if the soil is dry.
5. Cacti Safety
If you have children or pets in the house, cactus safety is critical. Even small cactus plants have sharp thorns that can damage tender flesh or an eye. Keep indoor cacti out of reach on a windowsill or ledge. Outdoors, plant them away from play areas and pathways. Wear gloves and protective eyewear when you handle cactus plants.