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An archive of gardening information assembled by Dr. Jerry Parsons to answer your questions - provided as a service by Texas Cooperative Extension

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Questions/Answers For "Christmas Cactus"

Question 1:

What can you tell me about Christmas cactus? How can I make mine bloom?

Answer:

The Christmas cactus is one of the favorite house plants for the holiday season. Other species of similar plants include the Thanksgiving cactus and the Easter Cactus. Christmas cactus is known by the scientific name Schlumbergera bridgesi. Thanksgiving cactus is known by the scientific name Schlumbergera truncatus. The latter of these two are distinguishable by prominently toothed joint margins and yellowish anthers. The Easter cactus blooms in the spring and is classified as either Schlumbergera gaertneri or Rhipsalidopsis gaertneri. Cultivars of these holiday cacti vary in flower color from white through pink and red to purple. Hybrid crosses are available and may exhibit growth characteristics and flowering similar to both parents. Flowering in holiday cacti is regulated by day length (photoperiod) and temperature. Christmas and Thanksgiving cacti will flower if grown under the influence of normally shortening fall days (just as poinsettias) and cool nights. Thanksgiving cactus will usually set buds as early as mid September, and Christmas cactus will have significant bud set by late October or early November. To ensure a Christmas flowering, give plants short days of 9-10 hours (14-15 hours darkness) starting September 15. During bud initiation, maintain night temperatures of 55-60 degrees. Flowering will occur at temperatures below 55 degrees, regardless of day length, but flowering will be erratic. Night time temperatures higher than 70 degrees inhibit bud development. Stressing plants by withholding water before initiation of short days may improve bud set. Do not withhold water during or after bud set; this will lead to abortion of buds and flowers or small flowers.

Depending on photoperiod exposure and temperature, the Christmas cactus should bloom late fall or early winter. Flower buds of Easter cactus develop more slowly and will not appear until late winter or early spring. After flowering is complete, the plants will produce new vegetative growth. This new growth will support flower buds for the next blooming period. During this active growth period, provide more fertilizer and water. Harden off new growth and increase opportunity for bud development in the fall by reducing irrigation and fertility in mid August.

Holiday cacti thrive in a well-drained, sterile potting medium that is high in organic matter. Sand may be added to increase the weight of the medium. As plants develop new branches and buds, they often become top heavy and difficult to handle. A soil pH of 5.5-6.2 is optimum for growth. Fertilize until flower bud initiation occurs. A good soluble fertilizer (such as 20-20-20) is recommended. Do not forget to apply trace elements. Allow soil to dry between waterings, but don't let it go 'bone dry.' Over-watering is a major problem on cactus. Leach the medium with plain water a couple times a month to flush out soluble salts. During the growing season, maintain temperatures of 70-80 degrees for ideal growth. Cactus will tolerate 90-100 degree temperatures, but vegetative growth may be reduced. Flower drop and lack of flowering are the most common problems with the holiday cactus. Follow the aforementioned guidelines to improve flowering. Flower bud drop is commonly caused by:
* excessive water
* inadequate water
* exposure to cold drafts (temperature changes)
* air pollution (stagnant air, non-vented heaters, etc.)
* over-fertilization
* rough handling

Insect pests, including mealy bugs and scales, are occasional problems on holiday cactus. To control, use a recommended insecticide. Repeat applications may be necessary. Follow the label instructions.

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