If you want last year's holiday cactus or poinsettia to bloom again, now is the time to take action. Because these plants bloom in response to shorter days and longer nights, you need to place them in complete darkness for approximately 15 hours every night from now until mid-December. A good rule of thumb is to cover them with a cardboard box at 5 p.m. and uncover them at 8 a.m. If they get even a small amount of light during the night (from a streetlight, for example), they may not flower properly.
Other tips for getting holiday cacti and poinsettias to rebloom:
- Keep night temperatures cool. Poinsettias do best when it's 55ºF to 70ºF at night, and holiday cacti like temperatures of about 50ºF to 60ºF.
- During the day, give plants bright, indirect sunlight.
- Water only when the soil is thoroughly dry.
- When plants begin to bloom, you can stop covering them at night