AMES, Iowa — While gardeners are busy with late summer garden chores and arranging mums for fall displays, they should also be planning ahead for Christmas blooms. Horticulturists with Iowa State University Extension and Outreach explain how to achieve perfectly timed Christmas cactus, poinsettia and amaryllis blooms. To have additional questions answered, contact the horticulturists at 515-294-3108 or firstname.lastname@example.org.
The Christmas cactus requires proper environmental conditions to flower. Critical factors in flower initiation are day-length and temperature. The Christmas cactus is a short-day plant. Short-day plants grow vegetatively during the long days of summer and produce flowers when days become shorter in fall. The Christmas cactus will not bloom properly if exposed to artificial light at night in fall. Flowers may also fail to develop if the plant is exposed to temperatures above 70 degrees Fahrenheit. Night temperatures of 60 to 65 degrees Fahrenheit with slightly warmer daytime temperatures are ideal for flower formation.
In late summer, 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. To avoid flower bud drop, do not move the plant during flower bud development. The Christmas cactus can be moved and displayed in another room when the first flowers begin to open.
Bring the amaryllis indoors in late September (before the first frost or freeze in fall). In order to bloom, amaryllis bulbs must be exposed to temperatures of 50 to 55 degrees Fahrenheit for a minimum of eight to ten weeks. This can be accomplished by inducing the plant to go dormant and then storing the dormant bulb at a temperature of 50 to 55 degrees Fahrenheit. To induce dormancy, place the amaryllis in a cool, semi-dark location when the plant is brought indoors in late September. Withhold water. Cut off the foliage when the leaves turn brown. Then place the dormant bulb in a 50 to 55 degree Fahrenheit location for at least eight to ten weeks. After the cool requirement has been met, start the growth cycle again by watering the bulb and placing it in a well-lit, 70 to 75 degree Fahrenheit location. Keep the potting soil moist, but not wet, until growth appears.
The other option is to place the plant in a well-lit, 50 to 55 degree Fahrenheit location in late September. Maintain the amaryllis as a green plant from fall to mid-winter. After the cool requirement has been met, move the plant to a warmer (70 to 75 degree Fahrenheit) location.
Poinsettias are short-day plants. Like the Christmas cactus, it grows vegetatively during the long days of summer and produces flowers when days become shorter in 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 eight 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 kind 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 two weeks during the forcing period. While poinsettias are difficult to flower in homes, proper care can reward home gardeners with a colorful plant for the holiday season.