Christmas Cactus (Schlumbergera Bridgesii)
by Tom Rood, Master Gardener
Cornell Cooperative Extension

Christmas Cactus, a native of Brazil, is a jungle forest type cacti and a truly a great flower to have in the home. It gets its name from its season of bloom. The plants have a wide flat stem that looks like a thick, long, segmented, green leaf. With proper care it is long-lived. One plant I read about was 67 years old. This is one holiday perennial that will grow all year long since it has no required dormant period. Blooms come in a wide range of colors, including the usual red, as well as salmon, pink, and white. They are easy plants to grow and strong growers for those gardeners who have only slightly green thumbs.

The plants like a bright location with some sunshine but too much sun may cause the leaves to turn yellow. Most growing is done between April and September and especially during warmer summer days when temperatures range between 70 and 80 degrees. Flower buds will begin to set in late September or October. After flower buds are formed, Christmas Cactus becomes more sensitive to light and doesn't seem to like changes in location. Therefore, find a permanent location from early fall onward that will give enough light for good growth and then leave the plant there through the blooming cycle. If it becomes necessary to move the plant, find a new location that nearly duplicates the original one. Otherwise, the flower buds may drop.

Christmas Cactus is a cacti that requires more water than most other cacti plants. The soil should be kept slightly moist all the time …on the dry side, not soaked, One way to test the moisture content is to use the finger test by digging down a half-inch below the surface with the fingers and feel for moisture. Never over-water these plants but when watering, use enough water to ensure the entire root ball is moistened. Some water leaching out of the pot's drainage holes is desirable and that excess should be removed when drainage is complete. Over-watering is one common fault with this plant. Water-logged roots may be one cause of early bud drop. Excessive dryness or high temperatures can be responsible for the same thing. The most care with watering must be done in late summer through early fall. This is when the flower buds are forming. Keep the plant on the dry side by applying just enough water to keep the leaf-like stems from shriveling. As soon as the buds are formed, begin watering normally.

Winter temperatures are cold of course, but it means that the molecules of air are squeezed into a tighter space reducing the amount of moisture it can hold. This same air enters the heated home and the molecular space expands. This causes the humidity to drop which is why heated air is always dryer. House plants, as well as wooden furniture, suffer from this reduced moisture content. If flower buds start to drop from low humidity levels in the room, place a tray of pebbles or aquarium gravel under the plant and keep the tray filled with water only to the surface of the gravel or stones. Do not let the pot itself stand in water. The tray might add enough humidity to help the plant. Or, you might take lots of showers and make lots of tea. Either of those two activities add moisture to the air. A mister spray bottle filled with distilled water and sprayed gently and lightly over the leaves will assist the plant in overcoming excessive
dryness, but don't over do it.

From late summer through early fall, withhold fertilizer to allow the plant to form flower buds. Once the buds are formed, a liquid fertilizer high in potassium can be applied every two weeks following the labeled directions. Do not allow the fertilizer to come in contact with foliage.

Flowering of Christmas Cactus grown indoors is related to the daily period of light (photoperiod) and day and nighttime temperatures. Plants left outside during the normal growing season will feel the effect of early Fall's shorter daylight periods and cooling temperatures which reach down to 50 to 55 degrees. The combination of lower light periods and cooling temperatures have the effect of starting flower buds to form. This may take place before the plant is brought indoors. One source mentions that Christmas Cactus grown outdoors before being brought inside, will, if left outdoors through Fall, receive enough cool 50 to 55 degree temperatures to set flower buds no matter how many dark hours the plant receives. In any event, the plant should be brought inside well before killing frost threatens. Even if grown in cool temperatures in the 60 to 65 degree range, plants brought inside before flower bud set will need a 13-hour dark period every night for several weeks as described below.

Plants grown indoors year 'round will need to have their photoperiod reduced artificially. This usually means removing all light from the plant for a period of 13 hours daily to force bud formation. This can be accomplished in several ways. A cool closet, or an unused/unlighted room with the heat turned off and shades pulled down may work to simulate darkness or you may achieve the same effect by covering the plant with a brown paper bag or dark towel. Large plants will require some covering that will block light and yet not crush the plant. Once flower buds have formed, normal treatment of the plant can be resumed. Remembering to cover and uncover the plant each and every day until flower buds are formed is a lot like walking the dog twice a day.

Keeping the plant in a cool location will lengthen its bloom period. If the plant begins to bloom too early, dropping the temperature should slow it down. Some plants seem to have difficulty blooming with all sorts of tender loving care while others respond wonderfully to zero attention. It all comes down to light, temperature, and moisture in the right amounts and at the right times. My mother would look at a plant that was sulking and say "Bloom or out you go!" and you know, the plant soon began blooming.

In Spring, after all frost danger is well past, as in late May, the Christmas Cactus may be taken outdoors. Set the pot in a semi-shaded area where it will receive good light but not much direct sunshine. Keep the soil moist throughout the growing season, fertilizing once every two weeks. Since the plant resides in the pot for such a long period, flush the potting soil with water periodically. This tends to carry away any toxic build-up from unused fertilizers or water residues. Be sure the pot drains thoroughly and quickly. Standing water around the roots encourages root rot. After flushing, let the plant reach the dry side before watering again. Remember to bring the plant back inside before killing frost occurs.

Christmas Cactus is one plant that should be allowed to become slightly root bound. Repotting is necessary once every three years and should be done after bloom. However, only move up one pot size. Over-sized pots will allow too many green stems and fewer flowers to be produced. A good humus potting mix is desirable, such as one that contains one part good garden soil, two parts peat moss, and one part sand. Leaving the plant root bound too long in one pot will be evidenced by reduced flowering.

Christmas Cactus responds to propagation through stem cuttings. The cuttings should be taken anytime but spring might be the best. Cuttings should come from the tip of stems. "Y" shaped stem cuttings seem to work best but most are capable of setting roots. Each cutting should have two or three jointed segments. Cuttings can be dusted with a rooting hormone powder. Allow the cuttings to lie on a dry surface for three to
four hours to form a callus and plant in a rooting medium such as damp sand. After four to six weeks, the cuttings should have formed roots and can be inserted into a moist sterile potting soil mix. Do not let the starter soil mix dry out or become water logged.

The secrets to success with Christmas Cactus is to keep in mind that it is a tropical jungle plant that grows under a canopy receiving only mottled or indirect sunlight. It must go through a wet/dry cycle with an abundant need for water from spring through fall. Once we understand this and the plant's need for a photoperiodic cycle, we have come a long way towards having a Christmas season filled with bright cacti blooms.

For all your lawn and garden questions, call the Master Gardeners at the Cooperative Extension office (315) 536-5123 leaving your name, question, phone number and a time we may return your call with the results of our research. If you are interested in becoming a Master Gardener, a new class will be forming in January. Call the Cooperative Extension Office for details.