Light & Temperature: The holiday cacti grow best in light shade. Full sunlight is beneficial during fall and winter, but bright sun during the summer months can make plants look pale and yellow. Ideal spring and summer growth occurs at temperatures between 70 to 80 °F during its growing season from April to September. During the fall, the Thanksgiving and Christmas cacti depend upon shorter day lengths (8 to 10 hours) and cooler temperatures to set their flower buds. Do not let temperatures rise above 90 °F once the flower buds are set in the fall. Continuous warm temperatures can cause flower buds to drop. Do not leave these cacti outside if temperatures will drop below 50 ºF.
The secret of good flower bud production during the fall involves temperature regulation and photoperiod (length of day and night) control. To initiate flower buds the plants need:
• Bright light.
• Long nights. Fourteen hours or more of continuous darkness each day is required before flower bud set will occur. Long nights
• Pinching back the stems in early June to promote branching and more terminals for more flowers.
• Pinching (also called leveling) at the end of September to remove any terminal phylloclades that are less than 1 cm (0.4 inch) long and to make all stems approximately the same length. These short and immature stem segments will not initiate flower buds until mature. After a short phylloclade is removed, a flower bud forms on the previous, more mature stem segment.
Watering & Fertilizer: Water the growing medium when it is dry to the touch. The holiday cacti are tolerant of dry, slightly under-watered conditions during the spring and summer. Do not let the soil become waterlogged, especially during the dark days of winter, but do not let the soil completely dry out either. However, following bud set in the fall, the growing medium must be kept evenly moist to prevent flower bud abscission. Never let water stand in the saucer beneath the pot.
Fertilize plants monthly from the time new growth starts in late winter or early spring, and throughout the summer using a one-half strength soluble fertilizer, such as a 20-10-20 or 20-20-20 with trace elements. Holiday cacti have a higher requirement for magnesium than many plants. Fertilize monthly during the growing season with Epsom salts (magnesium sulfate) mixed at 1 teaspoon per gallon of water, but do not apply the same week as the regular fertilizer. Stop fertilization during the late summer for greater flower bud production in the fall.
Growing Media: The holiday cacti flower best when kept somewhat pot bound. Repotting is necessary only about once every three years and is best done in the spring.
More next time about propagation Christmas Cactus.
James Blake, ©2011 HGIC, Clemson Extension
Taken from HGIC 2251, Houseplant Diseases & Disorders.
Revised by Joey Williamson, HGIC Horticulture Extension Agent, Clemson University (11/11). Originally prepared by Nancy Doubrava, HGIC Horticulture Specialist and Al Pertuit, Extension Floriculture Specialist, Clemson University. New 05/99. Image added
Till next time, this is Becky Litterer from Becky's Greenhouse, Dougherty, Iowa