University of Vermont
Department of Plant and Soil Science

Fall News Article


Dr. Leonard Perry, Horticulture Professor
University of Vermont

You have probably heard of the Christmas cactus, but did you know that there is also a Thanksgiving cactus which, as you've probably guessed, comes into bloom in November?  This houseplant doesn’t have spines, as its name may lead you to believe, has easy culture, and can live for many years. Some people have plants that were passed down from their mother or even grandmother.
You can tell the Thanksgiving cactus (Schlumbergera truncata) apart from the Christmas cactus (Schlumbergera bridgesii) from the shape of its leaves. The leaf segments, botanically termed “phylloclades”, are serrated or "toothed" on the former as compared to the more rounded leaf margins of the Christmas cactus. Also look at the pollen-bearing anthers—those on the former are yellow, those of the Christmas cactus are pink to purplish-brown.
You may see the Thanksgiving cactus listed by another older name (Zygocactus) in some older references.  These two species are native to coastal mountains of south-eastern Brazil, where they are found growing in trees (“epiphytic”) and on rocks (“epilithic”) in shady and humid conditions.  With their pendulous branches, they work well in hanging baskets.
There even is an Easter cactus (Rhipsalidopsis gaetneri), blooming of course in spring, whose leaf margins have small bristles, leaves are more three-dimensional with a thick ridge on one side, and flowers are more star-shaped than the other two cacti.  It is native to the natural non-tropical forests of Brazil.
Flowers of the Thanksgiving cactus and its relatives are produced from the tips, or from where the leaf segments join.  They’re quite unusual, resembling a long tube of a couple inches, appearing as if a flower within a flower.  Tops are different from the bottoms of each flower, termed “zygomorphic”. Flowers come in a range of colors, mostly pastels, including variations of red, pink, peach, purple, orange, or white.

To care for your Thanksgiving cactus, allow the soil to dry out during "resting periods," or in other words, when it is not producing blooms.  Water only when the soil is dry to the touch. Overwatering can kill the plant.  Provide plenty of indirect light and room temperatures of 60 to 65 degrees F. 

If you already have a Thanksgiving cactus from last year, to get it to bloom on time you’ll need to begin temperature and light treatments in mid-September.  It will need 12 to 14 hours of total darkness, along with cool nighttime temperatures of 60 to 65 degrees (F), for about three to four weeks in order to form buds.  When you see buds, you can go back to normal lighting, but keep plants cool.

The easiest way to achieve the light control is to place the plant in a closet from 6 p.m. to 8 a.m., just remember to bring it out each day.  Or you can cover the plant with a large brown paper bag.  As little as a couple hours of light during this dark period can negate your efforts.
If you keep the plant in a continuously cool room around 50 to 60 degrees (F) in September and October, chances are excellent that it will produce flowers, regardless of day length, growth though will be slower.  Buds may drop off, however, around 50 degrees or below. Since only the mature leaf segments produce buds, you may want to remove any immature ones that are less than about a half-inch long unless you want longer stems for future years.

Once buds start to form, apply houseplant fertilizer according to label directions to encourage lush growth and an abundance of blooms.  Too high a temperature, heat fluctuations (such as placement near heating vents), too dry, or too low a light level will cause buds to drop.  Keep evenly moist, but not overwatered or sitting in a saucer of water—this can lead to root rots and plant death.  They usually don’t get pests, but watch for the white cottony mealybugs.

Although Thanksgiving cactus like to be slightly pot bound, repot as needed to prevent plants from becoming too pot bound—about once every three years—which is best done in spring.  If they haven’t been repotted for years, they may have fewer or no blooms.   Since these cacti naturally grow in trees, they prefer a growing medium that is quite well-drained with good aeration, such as from about 60 percent potting soil (not garden soil) and 40 percent perlite.
When planted in a decorative pot, they make a nice gift, holiday table centerpiece, or present for friends and family.  Most garden stores, chain stores, and even grocers carry holiday cactus plants, although it is easy to grow them from cuttings if you have a plant already. 
To propagate, snip off a branch with four or five segments or sections of leaves.  It is usually a good idea to place the cutting where it will get good air circulation, out of direct sun, for a few days to allow the wound to begin healing before planting. 

To plant, push the root end of the cutting about one inch deep into potting soil, vermiculite, or damp sand.  The medium should be kept just barely moist, not wet.   To help prevent the soil from drying out, invert a plastic bag over the pot.   Use straws or popsicle sticks to keep the bag from resting on the foliage.  Vent frequently to keep from being too moist.

For best results, place the pot with cuttings in a spot that gets plenty of light but is out of direct sunlight.  You should see new growth in three to four weeks.  Don’t get too anxious to see flowers though on your newly rooted cutting, as it may take a couple years for the plant to mature sufficiently.

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