October 22, 2015 – Kenosha News
Question: I saved my poinsettia from last Christmas by moving it outdoors for the summer. This fall I brought it inside before the weather got cold. What should I do to get the poinsettia to bloom again? What about Christmas cactus? E.R.
Answer: Poinsettias are the most difficult of the traditional holiday plants to re-bloom. Poinsettias are semi-tropical and damaged by temperatures below 45 degrees Fahrenheit and rapid temperature changes.
Indoors keep your poinsettia in a bright, sunny, south window. Day and night temperatures should be 60 to 70 degrees. Night temperatures above 70 degrees will reduce or prevent flowering. Fertilize your poinsettia with a general purpose houseplant fertilizer every two weeks.
Poinsettia must have long nights (or short days) to initiate development of flower buds. If you want flowers by Christmas, you should immediately begin covering your plant with a light-tight box from 5 p.m. to 8 a.m. The plant must be uncovered during the day. Alternatively, you can put the plant in a closet every night and take it out every morning. The slightest bit of light in the dark period during these two months will prevent flower formation. The long night treatment can be discontinued after the colored bracts develop.
Thanksgiving and Christmas cacti require cool night temperatures and/or long nights to initiate flower buds. Place plants in a bright sunny location where the night temperature drops to 55 to 60 degrees. Daytime temperatures of 60 to 65 degrees are ideal. Under these conditions holiday cactus will bloom in five to six weeks.
If the temperature in your home at night is 60 to 65 degrees most types of holiday cacti will need at least 13 hours of uninterrupted dark for four to six weeks. The easiest way to make sure your plant has complete darkness is to cover it with a box every evening and uncover it every morning.
Night temperatures about 65 to 70 degrees usually prohibit flowering of holiday cacti regardless of the length of night.
Many gardeners are able to stimulate profuse flower production by keeping holiday cactus plants outdoors in a protected location until danger of frost. When brought indoors, the plants should be placed in a cool bright spot.
After your holiday cactus forms flower buds and begins blooming, reduce watering and do not fertilize.
Barb Larson is horticulture educator for the Kenosha County University of Wisconsin Extension. She holds a master’s of science in horticulture from the University of Wisconsin-Madison. If you have a plant or gardening question, email her at firstname.lastname@example.org or call 262-857-1942.