The problem with cacti with pricks is to keep them away from children and pets, as best as possible. They are lovely plants.
There are two varieties of cacti grown as houseplants, and both are popular and readily familiar. The desert cacti are the "traditional" cacti, usually covered with spines or hair and often growing in paddles, balls or obelisks. Forest cacti grow in wooded areas, ranging from temperate forests to subtropical and tropical regions. The most well-known forest cacti is probably the Christmas cactus. Both desert and forest cacti boast beautiful blooms, but they have very different growing habits.
The Desert Cacti
When I think cactus, I'm usually thinking about the desert cacti. These aren't friendly plants—grab a desert cactus without thinking about it and you're in for a nasty surprise. But they have a unique, stark beauty, and some of the desert cacti feature the most beautiful flowers in the plant kingdom. I had never thought of a desert as particularly lush until I saw my first desert bloom. There's nothing quite like it.
Growing desert cacti is not difficult—these are among the toughest of all houseplants—but it does require sticking to some pretty simple rules. There are dozens of kinds of desert cacti on the market today—for the most part, the rules governing their growth are the same. Some species of cacti will bloom after 3 or 4 years in cultivation. Others will take longer, or never bloom indoors. Generally, follow these tips for success with desert cacti:
Light: Strong light is essential for healthy cacti, especially in the winter. Some species may scorch in direct summer sun if they haven't been hardened off first.
Temperature: During the active growth period, cacti prefer hot, dry temperatures, ranging from 70ºF to more than 80ºF. In the winter, the plants prefer a cooler period, down to 55ºF. In their desert habitats, many cacti are accustomed to very chilly nights. However, protect them from very cold winter drafts.
Water: In the spring and summer, when the plant is actively growing and/or blooming, water whenever the compost begins to dry. During these watering, make sure the plant is thoroughly watered. During the winter rest period, nearly cease watering. Only water, if the plant begins to shrivel.
Potting Soils and Repotting: Pot into a fast-draining cacti mix. If one is not available, amend regular potting soil with inorganic agents like perlite to increase drainage and aeration. Cacti are generally slow-growing plants and will rarely need repotting. Also, remember that many species of cacti will bloom better when they are slightly under potted.
Fertilizer: Use a cacti fertilizer during the growing season. Some growers have poor results with standard fertilizers, so it's probably worth it to seek out a specialized cacti fertilizer.
Common Problems: The most common mistake with desert cacti is overwatering in the winter, which will cause rot either at the base of the plant or at the tips of the growing areas. If the rot is advanced, it might be necessary to start new plants from cuttings or discard the whole plant. Cacti are also susceptible to pests include mealy bugs and mites.
The Forest Cacti
The forest cacti grow in tropical and subtropical regions throughout the world. They are often climbing or epiphytic plants that cling to trees. The most famous among these is the Christmas cactus, which is native to Brazil. Today, Christmas cacti are available with blooms in red, pink, purlpe and even yellow. They make excellent hanging plants.
Light: These plants like bright, but not direct, sunlight. Move them outside during the summer (see Blooming Tips below).
Temperature: During the growing season, they have a wide range, from 55ºF to 70ºF. During the rest period, a colder spell of 50ºF is essential.
Water: Water as a normal houseplant during the summer months and when the buds begin to show. During the resting period, only water when the soil is dry to the touch.
Potting Soils and Repotting: Use a regular potting mix. Repot at the beginning of the growing season.
Fertilizer: Fertilize during the growing season with a standard fertilizer. Reduce fertilizer during the growing season.
Blooming Tips for Christmas Cacti: Coaxing multiple blooms from a Christmas cactus (or the closely related Easter cactus) takes a little planning. Before you want the plant to flower, cut it back and induce a rest period when watering and fertilizer is reduced and the plant is kept cool (about 50ºF to 55ºF). After one to two months, move the plant to a warmer place and resume watering, and buds will soon begin to show. It is also essential to move the plant outside during the summer.
Common Problems: As with succulents and desert cacti, these plants should not be watered heavily during the rest period. Root rot will result. Advanced root rot can only be treated by taking new cuttings and starting over. Fortunately, these plants root easily from cutting. Failure to bloom is usually caused by an inadequate rest period and/or not taking the plant outside during the summer months.