Christmas Cactus

Eastern Prickly Pear Cactus (*Opuntia humifusa*) can be found in Ontario near Point Pelee

Hariette Henry & Janet Mackey – Halton Master Gardeners

Many of us hear the word cactus and assume they originate in hot, dry and arid regions, however there are many types of cacti that grow in a wide variety of settings. In fact we have a native cactus that grows right here in Ontario! The Eastern Prickly Pear cactus (Opuntia humifusa) can be found growing in natural areas with sandy soil, along the shores of Lake Erie near Point Pelee. There are also 3 other species of cacti that are native to various regions of Canada (Escobaria vivipara, Opuntia fragilis, O. polyacantha).

Christmas cacti (Schlumbergera bridgesii) in their natural setting, are epiphytes, meaning they don’t actually grow in soil on the ground, but get their nutrients from the air and water around them, as well as from debris that collects on a surface such as those found in the cracks and crevices of tree branches. Even more amazing though, these cacti grow on trees located in the rain forests of the southeastern coastal mountains of Brazil. Knowing their origins, can help us understand how to care for them in our homes.

Christmas cactus actually have no ‘true leaves’. The flattened stem segments called phylloclades. are rounded with 2-4 projections along the margins. Photosynthesis occurs within the green phylloclades (stems) and the flowers grow at the end of the phylloclades. Fortunately, unlike many other cacti, Christmas cactus does not have sharp spines.

The origin of the many plants sold in the horticultural industry as Christmas Cactus can be a bit of a mystery. Most of the popular holiday cacti available today are cultivars of the genus Schlumbergera, rather than species. Some are called ‘Holiday Cactus’. This can include not only Christmas cactus, but also Thanksgiving cactus and Easter cactus which are each named because of the timing of their bloom. So much hybridization has taken place it can be difficult to distinguish the original species. Some of the hybridization has been done in order to achive longer bloom periods or develop new colours (white, pink, red, scarlet magenta yellow, orange, apricot, salmon, and even bicolors) . Hybrids are also developed to create a more upright plant while traditionally most of the older varieties spill downwards out of their container. Other hybrids may lengthen the show of flowers, but this can be manipulated by growers through careful use of light and temperature. If you purchase a new ‘Holiday’ cactus this year, you may not be able to know for sure what type it is until it blooms the following season.

By examining the shape of the stems (phylloclades or ‘leaves’) you may find clues as to which type of cactus you have. Christmas cactus (the cultivar that blooms during the Christmas season) falls within the Buckleyi Group which features stem segments with smooth, rounded edges, more or less symmetrical flowers which hang down, and pollen which is pink. The Thanksgiving cactus stems look like claws and are sometimes referred to as the Crab’s Claw or Lobster Cactus. Easter cacti have bristles at the end of each leaf and in between the segment joints.

Distinguishing between the species can be challenging: Check the shape of the **stems** (phylloclades) that resemble leaves. Image: Empress of Dirt

Holiday cactus plants are noted for having a long life span. I can personally attest to this as the plant in the attached photo was first owned by my mother. She cared for it for forty years until she passed away in 1988. At that point my sister took over and continued its care until today. She has also given cuttings to her two daughters and they each have a plant.

The 70 ‘plus’ year old cactus passed down to family.

Care

Christmas cactus is adaptable to most soil conditions and it will thrive in a cactus mix or in a general-purpose potting soil. To achieve optimal growth, it prefers a pH level between 5.5 and 6.2. Peat moss is a helpful additive to achieve a more acidic environment.

These plants are more tolerant of drought than many, but can be damaged by both under and over watering. Keeping the growing medium just moist throughout the year avoids either extreme. If you notice the stems beginning to shrivel it is a sign that the plant is dry.

They require bright light to flower but they can also be damaged by exposure to direct sunlight, stems taking on a reddish colouration is a signal to move the plant to a shadier spot. If you wish to place your plant outside during the summer months be careful to protect it from too much sun.

Propagation can be achieved by using short pieces of stem, one to three segments long, twisted off rather than cut. Cuttings are allowed to dry for 1–7 days, forming a callus at the broken end, and then rooted in an open growing medium. Temperatures above 21 °C (70 °F) and up to 27 °C (81 °F) in long day/short night conditions speed rooting.

Temperature and day length provide crucial bloom triggers for the Christmas cactus. The term for this response is thermo-photoperiodic. Flower buds will form if one of the following conditions is met:

a cool night temperature around 10 ºC
13 hours of uninterrupted darkness (if temperature is between 10 and 20 ºC)
15 hours of darkness (if temperature is above 20 ºC)

Plants should be on the dry side until you see pin-point buds forming. When buds appear, increase the number of times you water, but not the volume of water used. Too much water may cause buds to fall. After the plant has flowered, prune back each stem by pinching off enough sections to achieve a uniform habit. Resume normal watering and fertilization when new growth appears.

Problems:

bud drop – a wide range of causes which can inclue: high temperatures, exposures to drafts, lack of light, under/over watering, low humidity or exposure to fumes from gas burning stoves
shrivelled & drooping – plant has been left to dry out causing some roots to die back followed by the caring plant owner trying to rescue it by over-watering. To revive, water more frequently, BUT with SMALL amounts of water each time.
blister-like water filled swellings on the stems – these can burst leaving a dry corky spot: over-watering is usually the cause. Water only when dry but not descicated.
Mealy bugs, scale, spider mites and aphids – usually only occur if they are in an outdoor environment over the growing season. Inspect carefully before bringing them indoors and treat with insecticidal soap if necessary (NOT a dish soap mixture).