Q. What is the difference in a Christmas and Thanksgiving cacti care?
This is a pretty common problem since the two species that are sold as Christmas cactus have specific requirements in order to bloom. (Christmas cactus - Schlumbergera bridgesii - has flattened leaves with rounded teeth on the margins; the leaves of Thanksgiving cactus - Schlumbergera truncata - have serrated edges. Their common names indicate their natural bloom times.) To set buds and produce a full bloom these plants must have short days and/or cool temperatures. They also do best with thorough but infrequent waterings during the bud-forming phase.
Flower buds will form if one of the following conditions is met:
- cool night temperatures between 50 to 55 degrees
- 13 hours of uninterrupted darkness (if the temperature is between 55 and 70 degrees)
- 15 hours of darkness (if the temperature is above 70 degrees)
Uninterrupted darkness means absolutely no light during the dark period, including lamp light. You can achieve this by covering the cactus with a black cloth or plastic bag, or placing it in a closet or unused room during the dark hours.
Count backward eight weeks from the approximate date you would want the plant to bloom to determine when to begin the light/temperature restrictions. When buds appear, increase the number of times you water, but not the volume of water used. Too much water may cause buds to fall off, as will moving the pot around. (Who knew these plants were so picky?)
Once they start flowering plants will produce blooms for four to six weeks. After flowering is done prune back each stem by pinching off enough sections to achieve a uniform habit. Resume normal watering and fertilization when new growth appears.