Extension Educator, Horticulture
For years I have heard the frantic calls of Christmas cactus caretakers. Nobody wants to be the descendant that killed grandma's Christmas cacti. My suggestion – give lots of stem cuttings to your relatives. It's always best to spread the pressure around.
Holiday cacti are known for their colorful tubular flowers and ease of care. They include Christmas, Thanksgiving and Easter cacti. Christmas cacti have flattened leaves with rounded teeth on the margins as opposed to the Thanksgiving cactus that has pointed teeth. Easter cacti have pointed teeth with fibrous hairs in the leaf joints. Under normal conditions the holiday cacti will bloom close to the holiday suggested in its name. Florists will often force plants into bloom at other times. To make things really confusing, most of the Christmas cactus sold are actually Thanksgiving cactus and will bloom in subsequent years at Thanksgiving time. So don't be surprised if the plant you bought last year at Christmas time is blooming now.
Holiday cacti are easy to care for once you realize they are not the sun-loving, drought-loving cacti of the desert. In their native range they live in the rain forest of the Organ Mountains of Brazil. As epiphytes they live in tree branches happily rooted in accumulated organic debris with rainfall amounts varying from a whopping 17 inches per month in December through March to just 3 inches per month in the subsequent dry season.
A common concern is the holiday cactus no longer blooms. Getting them into flower requires a little understanding of what makes them tick. Holiday cacti are short day plants meaning they bloom when nights are at least 14 hours long and daylight periods are between 8-10 hours for 6 weeks. Streetlights or indoor lighting may disrupt the required dark period so they may need to be covered each night. Holiday cacti will also flower if exposed to prolonged cool temperatures between 50-55 degrees F. No flowers will form at night temperatures above 68 degrees F regardless of light length.
Holiday cacti can be placed in a shady spot in the garden in summer. I just leave mine outside or in an unheated porch until temperatures get below 50 degrees. The naturally longer nights and cool temperatures in late summer will encourage flower development. Grandma may have virtually ignored them in a spare bedroom or garage where temperatures were cool and no lights were used at night.
Once plants are in flower, they should be kept in bright, indirect light. Day temperatures of 70 degrees F and evening temperatures of 60-65 degrees F are considered ideal. Be sure to water thoroughly, but let plant dry slightly between waterings. It is especially important not to let soil dry too much during flowering.
Once flowers fade, continue to grow the plant as a houseplant. Soil should be well drained and most container soils will work. Fertilize monthly between April and October with a complete houseplant fertilizer. Prune plants in June to encourage branching and more flowers. Just remove a few sections of each stem with your fingers or a sharp knife. The removed pieces can be rooted in moist vermiculite to make more plants.
A common problem with Christmas cacti is dropping unopened flower buds, which may be caused by low humidity, a sudden change in temperature or light, or soil that is too dry. The most common insect pests are mealybugs and soft brown scale. The major disease is stem and root rot. Plants appear wilted and dull gray-green with water-soaked dead areas near the soil line often with faded reddish margins. Stem leaves often fall off. Avoiding excessive watering to prevent. Cut out infected areas, repot into clean soil and hope your relatives have had more success.