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Botanist Marie Clark Taylor and the Impact of Light on Plant Processes: Growing Holiday Cactus

Schlumbergera photo courtesy of Flickr cc/JAM343
Schlumbergera; photo courtesy of Flickr cc/ JAM 343
 

Tropical forest (or jungle) cacti typically originate as epiphytes or lithophytes, growing in a pocket of moss or debris in the crook of a tree branch or a rock. So despite the humid  conditions of their native habitats, these cacti are adapted to grow in a media that is prone to dryness. Tropical forest cacti are succulents, with areoles containing often-tiny bristles, but differ considerably in appearance from desert cacti. They are usually leafless, composed of flattened or tubular segments and kept for their attractive flowers more than their architecture.

Some of the tropical forest cacti have become very popular as houseplants and are widely sold though often under confusing names. The true Christmas cactus is Schlumbergera x buckleyi which typically blooms in December, has purple anthers (the part of the plant that contains the pollen) and has been available for many years. More recently, Schlumbergera truncata in particular has been widely produced and sold as Christmas cactus, holiday cactus or Thanksgiving cactus. Holiday cactus is an apt name, as these plants tend to bloom from November to January.  They can also be differentiated from S. buckleyi by the sharper points to their serrated leaves and their yellow anthers. Compounding the confusion, there are numerous botanical synonyms also in use for these plants, with many nurseries continuing to use the Zygocactus genus that has been out of botanical use since the 1950's.

CARING FOR HOLIDAY CACTUS

Keep in mind that some variation in light and temperature routine during the year is recommended.  These cultivation rules are described below under Encouraging Your Holiday Cactus to Flower.

Light

Imagine the understory, filtered light of a tropical cacti’s natural habitat. These plants prefer a medium source of light year-round and will die if exposed to prolonged, direct, summer sun. Morning sun only is ideal, though they will survive less than ideal light exposures. Rotating the plant is beneficial but not essential. In some cacti, prolonged sunlight triggers flowering and you may need to simulate brighter conditions to get your plant to bloom. In others, a period of relative darkness is necessary to encourage buds.

Water

Water frequently in spring and summer, keeping the soil consistently moist but not standing in water run-off. Watering frequency should vary as your house heats up and cools down with the seasons. During the pre-flowering period, reduce watering, letting the top ½ inch of soil dry out between waterings. After flowering, water only enough to keep soil barely moist for a period of three to six weeks. Do not overwater; if your plant begins to turn yellow at the tips you are giving it too much water and causing the cellular structure to rupture.

Temperature

Holiday cacti like warm household temperatures all year, but need a rest period after flowering and while setting buds to re-bloom. They are less actively growing in some parts of the year but, unlike desert cacti, do not take a single, long winter rest in a much cooler space. To form flowers holiday cacti  need to be moved to a spot with lower temperatures (below 65° F.) for a month or two after flowering and again before setting buds.  Do not expose them to temperatures below 50°F. Spray holiday cacti daily to compensate for the inhospitable dryness of a Northeastern home.

Soil and Potting

Holiday cacti prefer a rich soil with excellent drainage. Many commercial cacti and potting soil mixes rely too heavily on peat, which holds moisture in the soil longer than is desirable for these plants. In general, mixing one part perlite (for drainage) with one part potting soil, one part peat and one part coarse orchid bark (for structure and nutrition) creates an excellent soil for your holiday cacti. You will notice that while this mix is fast draining, it will hold more moisture than a desert cactus mix. Plants that are potted in the wrong mixture will initially do well but may later suffer from root rot associated with excess water retention in the soil.

Repotting your plant annually after flowering is beneficial. Generally, a clean pot of the same size with fresh soil is fine as slightly tight conditions benefit flowering. You can also prune your cactus at this time to improve its shape.

Hatiora gaertneri (Easter cactus) flower; photo courtesy of Flickr cc/John Rusk
Hatiora gaertneri (Easter cactus), a close relative of holiday cactus, with more rounded teeth to the leaf margins; photo courtesy of Flickr cc/John Rusk

Nutrition

When flower buds begin to form, use a tomato-type fertilizer every two weeks through the flowering period and then stop. Do not use a high nitrogen fertilizer on these plants or any other succulent.

A Summer Holiday?

Tropical forest cacti benefit from the air circulation when placed outdoors during the summer months but keep them in the light shade.  The stems will harden with this outdoor exposure and your chance of a strong flower display will improve.

Encouraging Your Holiday Cactus to Flower

Holiday  cacti are the most common tropical forest cacti houseplants and these are generally purchased for their lovely flower displays. While they are easy and forgiving plants, there are some care rules that improve the chance of good flower production.

These plants do best if they have a period of rest after they finish blooming of a month or two and they need to experience lower temperatures and longer nights to set new buds. If your holiday cactus will not re-bloom, it is most likely that one of these elements has been missed in its yearly routine. In particular, your holiday cactus will not set buds if kept at normal household temperatures above 68° F. in the bud formation period.  Bud formation and bloom are also inhibited by the presence of artificial light at night, so household lamplight and even streetlights can be a problem.

A holiday cactus  typically flowers from late November to January. During the flowering period, keep temperatures above 60°F and water normally. Your cactus then needs a rest period for about two months following flowering. During this time the cactus should be watered  less frequently and kept relatively cool (around 55°F). Around April, you can increase water, temperature and re-start your feeding program. About two months before bloom-time, (mid-September)  keep your plant dry-ish and cool again until buds form, at which point you can resume regular watering.

Propagation

To propagate holiday cactus, cut off a section of stem with two or more segments at a joining point. Use the potting mixture described above and insert the cut end of the cactus gently into a pot of prepared soil. You can start several cuttings in a single pot and treat the cuttings as adult plants. No hardening of wounds is necessary with this type of plant.

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