If the temperature is lower than 60 degrees, plants set flower buds regardless of the length of the day or night. If the temperature is more moderate, plants show a classic short-day response. They initiate blooms as the days get shorter in the fall. Thanksgiving cactus has a 12-hour critical night length, meaning if it receives more than 12 hours of light in a day, it will not bloom. The vernal equinox occurs on Sept. 21, so all days after that date have less than 12 hours of light, which triggers trigger flowering.
Plants also respond to the cooler days.
After exposure to either cool temperatures or short days for six weeks, flower buds will appear. A number of researchers have looked at this practice and found it actually decreases bloom numbers. On average, the number of blooms per cladophyll was 2.5 for plants kept uniformly moist and 1.5 for plants exposed to a dry-down treatment. The Thanksgiving cactus should have a good, well-drained potting media. It's best kept somewhat confined, so only transplant the plants to a larger pot about every other year.