Christmas Cacti
Desert cactus (Cactaceae spp.) live in the hot, dry desert and need little water. That's why it's important to remember that Christmas cacti are not desert cacti. They are actually epiphytes that live in tree branches. Rather than seeking dry, hot sand, their native realm is the rain forest in Brazil. They like humidity and plenty of water. Water whenever the top inch of soil is dry.
Christmas cacti thrive outdoors in U.S. Department of Agriculture plant hardiness zones 9b through 11, but the vast majority of them live in pots indoors. These plants have been bred to bloom around a particular holiday, so you'll find Christmas, Thanksgiving and Easter cactus plants in commerce. But the majority of plants sold as Christmas cacti actually are Thanksgiving-blooming plants.
All of these types of holiday "cacti" require a potting soil that drains extremely well. They also need a pot with plenty of drain holes. To get the plant to bloom at Christmas, start in the fall by keeping its temperatures cool. When October comes around, give it indirect bright light during the day and total darkness at night for 12 or 13 hours.
Transplanting Christmas Cacti
You may like a little elbow room and feel out of sorts when you are too crowded. But that doesn't mean your houseplants have the same proclivities. A Christmas cactus plant likes feeling a little cramped and flowers best when rootbound. So don't be in a rush to get it into a bigger pot. Consider transplanting it every three to five years.
When the cactus's roots are crammed into the pot, it may be time to think about transplanting. The cactus will tell you when it's time by starting to look limp and tired. Repot the plant in February, March or April, but don't overplay the container size. Choose a pot about one inch bigger in diameter than the plant's old pot; use a potting soil with a high proportion of organic matter like peat or compost, and some coarse sand added. Alternatively, pick a soil specifically for cacti.
Carefully remove the Christmas cactus from its pot and brush or wash off the old soil. Tuck it into the new pot and add soil to the same level as in the prior pot, watering well when you are done.
What if you break off a stem while you are moving your plant to a new container? No problem. Put it in a pot of the same soil, and keep it moist. Place the pot in bright indirect light and watch your new little plant grow. Rooting cuttings is the best way to propagate these cacti.
Source: sfgate.com
