A Christmas cactus that is still showing only green leaves in November may still have time to bloom in December. The plant needs specific conditions to start budding, including long, dark nights and cooler temperatures.
Provide 12 to 14 hours of uninterrupted darkness each evening. A stray light from a hallway or television can disrupt the cycle, so the plant can be moved to a dark room or covered with a light-blocking box. Keep overnight temperatures around 55°F to 60°F (13°C to 16°C), then return the cactus to bright, indirect light during the day.
Water when the top inch of soil feels dry, and empty any water left in the saucer. The soil should stay lightly and consistently moist, rather than waterlogged or completely dry, as either extreme can harm roots or developing buds.
Stop applying fertilizer in late fall and avoid repotting until spring. Christmas cacti can bloom well when slightly root-bound, and disturbing the roots at this stage may stress the plant.
Once buds appear, keep the pot in one place. Rotating it, moving it to another windowsill or exposing it to drafts can cause the buds to drop. Choose a spot with indirect light, away from radiators and open windows, and leave the plant there until the flowers open.
Sources: Tom's Guide.