Q. How do I get my Christmas cactus to bloom? I was given a 9" pot back in November, kept it indoors with plenty of light, only to find out that it's supposed to be in the dark for 14 hours a day. I started that 3 weeks ago, been watering once a week, gave it cacti food twice, but no blooms.
A. The Christmas cactus is a true cactus and nearly identical to the Thanksgiving cactus. These cacti have slightly different bloom times so they get the names Christmas and Thanksgiving cactus because of their bloom times.
The amount of light (actually it's amount of darkness) will typically get them to bloom if all the light they receive is natural daylight. It's when they receive extra light inside the home that it can break this rhythm of flowering and cause them not to flower at this time of year.
These cacti bloom when the nighttime darkness approaches what we get a minimum of 12 hours of darkness. So if they are growing inside they need to be covered so they receive no light from artificial sources. Once covered they will bloom if they remain covered, religiously, for six weeks . They also respond to cool temperatures. So placing them in a colder location in the dark also will help them to bloom.
Christmas cactus is what we call an epiphytic cactus which means it does not grow in the soil in the wild but on the surface of other plants such as trees. We can however put them in containers and grow them in containers with soils amended with lots of truce one compost, similar to what they would find growing on the surface of a limb in the tropics. This is much like orchids and bromeliads. These cacti can be grown outside here on the northern or eastern exposure in a well amended soil or in containers but you must bring them in if there is any chance of freezing temperatures.