In 10 weeks, Christmas will be upon us. How do we encourage Christmas cacti and poinsettias to bloom in time for the holidays?
Christmas cacti and poinsettia flowers are initiated by 10 weeks of long nights (14 to 15 hours) and short days (nine to 10 hours). Nursery growers put black-out cloths over their plants to eliminate all light. Even a streetlight or a night light can prevent flowering.
If your plant will be in a room that receives light at night, cover it completely at 5 p.m. every day with a heavy paper bag or a piece of opaque black cloth or plastic. Or, place it in a dark closet at 5 p.m. each day, and do not uncover it until 8 a.m. Return it to a bright location each day.
Completely dark periods are necessary for the flowers to set. Flowers take 60 to 85 days to mature, depending on what variety they are, the temperature, and the daytime light intensity. Once the flowers begin to show color, it is less important to keep them in the dark at night. However, it is best to keep them in the dark at night until the flowers almost fully expand.
Temperatures should be 55 F at night and not more than 70 F during the day. Warmer nights will prevent flower bud initiation, and warmer days will shorten the flower life after they have developed. Keeping the plant cool at night (55 F to 60 F) also lengthens the blooming period.
Poinsettias do best with very bright sunlight. Christmas cacti prefer bright, but indirect, light. Do not let the plants touch cold windowpanes, and avoid drafts of warm or cool air.
Plants thrive with evenly moist, well-drained soil that is allowed to dry out slightly between watering. Do not let water stand in the pots or saucers. Clay pots are ideal because they allow the soil to breath.
Lightly fertilize your plants every 10 days with a liquid houseplant, tomato, or flower fertilizer until the flower buds develop.
Do not fertilize plants when they are flowering.
If your plants lose their flowers before they bloom, you may be over- or under watering them, or over fertilizing them with too much nitrogen. Drafts and temperature fluctuations can also cause flowers to drop prematurely.
Start the night-lengthening trick for your Christmas cactus and poinsettias now, and you will enjoy beautiful blooms at holiday time.
For more information, e-mail skellyj@unce.unr.edu or call me at 887-2252. You can "Ask a Master Gardener" by e-mailing mastergardeners@unce.unr.edu or call your local University of Nevada Cooperative Extension office. Check out many useful horticulture publications at www.unce.unr.edu.
- JoAnne Skelly is the Carson City/Storey County Extension educator for University of Nevada Cooperative Extension.
