In order to bloom during the upcoming holiday season, the poinsettia and Christmas cactus must be given proper care this fall.
Poinsettias are short-day plants. Short-day plants grow vegetatively during the long days of summer and produce flowers when days become shorter in the fall. In order for poinsettias to flower for Christmas, they must receive complete darkness from 5 p.m. to 8 a.m. each day from early October until the bracts show good color, usually around early December. (Most poinsettia varieties require 8 to 10 weeks of short days to flower.) Gardeners can protect their plants from light by placing them in a closet or by covering with a cardboard box. When using cardboard boxes, cover any openings to insure complete darkness. Exposure to any type of light between 5 p.m. and 8 a.m. will delay or possibly prevent flowering. During the remainder of the day, the poinsettias should be placed in a sunny south window. Keep the plants well-watered and fertilize every 2 weeks during the forcing period.
Day-length and temperature control the flowering of the Christmas cactus. Like the poinsettia, the Christmas cactus is a short-day plant. Plants will not bloom properly if exposed to artificial light at night. Flowers may also fail to develop if the plant is exposed to temperatures above 70ºF. Night temperatures of 60 to 65ºF with slightly warmer daytime temperatures are ideal for flower formation. In late summer/early fall, place the Christmas cactus in a cool location that receives bright light during the day, but no artificial light at night. An unused bedroom or basement may have the proper environmental conditions. Keep the Christmas cactus a bit on the dry side in fall. A thorough watering every 7 to 10 days is usually sufficient. Continue to give the Christmas cactus good, consistent care during flower bud development. Moving plants from one location to another, excessive watering, or other marked changes to their care during flower bud development may cause the buds to drop off. The Christmas cactus can be moved and displayed in another room when the first flowers begin to open.