These flat-leaved plants with pretty and normally red flowers are everywhere during the holiday season. Most folks see one and call it a Christmas cactus. Actually, many are Thanksgiving cacti.
The true Thanksgiving cactus (Schlumbergera truncata) usually blooms earlier and has leaves with points on them. Some people call that type ‘crab cactus.’ Christmas cactus (Schlumbergera bridgesii) has more rounded leaves and usually blooms a few weeks later. In the wild, both are rainforest epiphytes, which means they usually grow on other plants.
There is still another similar species called Easter cactus that usually blooms in spring. It has rounded leaf edges like Christmas cactus, and its blooming is more dependent on soil moisture levels.
Both Christmas and Thanksgiving cactus have photoperiod requirements. That means they must be exposed to a critical short daylength for a few weeks or they won’t initiate flowering. Temperature is important also. Night temperatures of 55 to 60 degrees are ideal for flowering.
Initiating buds doesn’t mean they will develop. Temperature and moisture levels have a lot to do with that. That’s why we can get a pretty specimen with buds in the fall only to have it drop all its flower buds by Thanksgiving or Christmas.
On the positive side, once buds are evident, daylength is no longer important. That’s good, because your plant is probably in an environment where it receives more than 12 hours of light per day. It also is exposed to night temperatures above 60.
If you recently bought or were given one of these plants, there are four main things to remember if you want it to thrive. First, give it plenty of light but keep it out of direct sunlight. Second, don’t fertilize it. That should be done in spring. Third, keep it in an area where it won’t get too hot, and finally, don’t overwater it but don’t let it dry out.
All these conditions probably explain why many folks buy a new one every year. Wet soil is usually the biggest killer followed by improper lighting. Moving plants is always a risk as well.
Long-term care requirements of both Thanksgiving and Christmas cacti are different from most plants. They grow better if they are rootbound, so don’t feel you have to repot them very often. Always avoid repotting them while they are in bloom.
Plants shouldn’t be pruned when they are blooming either. After blooming they can benefit from some heading back, but this is only if they are in a high light situation. Pruning encourages growth and low light levels will cause weak growth. This is true for most of your houseplants.
In summer, these cousins can be placed outdoors out of direct sunlight. This is the time to fertilize them. Next fall, around the equinox, remember to place them in a location where additional light can be avoided for at least four weeks.
This will enable them to bloom at the proper time. If you are a little late, your Thanksgiving cacti will bloom at Christmas and not Thanksgiving. Is that really so bad?
Ted Manzer teaches agriculture at Northeastern High School.