Re-blooming Holiday Cacti

Fall is the time of the year when those of use who still have the holiday cactus we received for Christmas last year need to give it special treatment to force it into bloom. Reblooming holiday cacti can be a bit challenging and a knowledge of its cultural requirements is vital for success.

Holiday cacti are short-day (long night) plants that need a long, uninterrupted period of darkness to be induced to bloom. The response they show to day length, however, is modified by temperature. Indeed, flowering will occur regardless of day length if it is exposed to night temperatures of 50-55 degrees. Unfortunately for our cacti, this is a temperature considerably lower than most people maintain in their homes. Most prolific flowering of holiday cactus occurs when plants are exposed to short days with at least 13 hours of darkness each night and cool night temperatures. Therefore, beginning in mid-October, place your cactus in a location where it receives no artificial light from sundown to sunrise the next morning and continue this regimen until buds start to form. Holiday cacti are native to a small region north of Rio de Janeiro, Brazil where they experience a "wet season" from December until March and a "dry season" for the remaining months. Reducing the amount of water to slightly stress the plant at the time it is exposed to short days will aid in the flowering process. In summary, subjecting holiday cacti to short days, cool nights and dry conditions in mid-October will cause plants to be in full bloom for the holiday season.

Holiday cacti commonly drop unopened flower buds when suddenly stressed. This can be the result of a sudden change in temperature, light or other environmental factors such as excessive drying of the growing medium. Poor flowering is often due to stray light interrupting the required long, uninterrupted period of darkness during short day treatment. Interior lights in the home, street lights or even car lights can disrupt the required dark period and cause disappointing flowering. Additionally, holiday cacti are very prone to root rot, which can lead to bud drop and plant loss. This can be prevented by avoiding excess watering and maintaining strict sanitation when culturing the plant. Holiday cacti should be kept slightly pot-bound to induce prolific flowering. When re-potting becomes necessary (about every three years), the growing medium used should be very porous and well-drained. Commercially available peat-lite mixes formulated for epiphytes are good choices. Regular peat-lite mixes can be made into epiphytic mixes by incorporating additional amounts of perlite or sterile sharp sand to increase porosity.

Given proper care, holiday cacti provide years of brilliant color around the Thanksgiving and Christmas holidays. The small amount of effort required by these plants is well worth it when one considers the reward of seeing an "heirloom" plant bloom year after year.

David Trinklein
Associate Professor Plant Sciences