The Anti-Christmas Cactus

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Ever get a pretty little Christmas Cactus as a gift, and wonder why it didn’t bloom the following Christmas?  It’s not being anti-holiday, it’s just tired.

The most likely problem is that your cactus is suffering from a type of insomnia.  Days in sunlight and long evenings in artificial light have robbed it of the ability to go into a period of light dormancy – or rest – which it desperately needs in order to gather enough energy to bloom again.

Circadian rhythm sleep disorders, as we all know, can really do a bang up job of messing with our energy levels.  In the case of plants – which, by the way, also have circadian rhythms – messing with their energy interferes with their basic functions, like: dormancy, budding, blooming, and forming seeds.  Just as some humans are severely affected by erratic schedules and alternating time zones, some plants are very sensitive to it as well.

Yep.  You guessed it.  The Christmas Cactus is one of these.  The problem lies in something called photoperiodism.

Photoperiodism refers to the physical effect on plants of alternating light and dark periods.  Perhaps you’ve heard the terms “short-day plants” and “long-day plants” before, and found it all confusing… but in essence, those terms are just labels meant to tell you which plants are particularly sensitive about how much light they receive – and most importantly – how much darkness they receive.

Long-day plants flower when the daylight lengthens and the darkness of night shortens below a specific threshold – triggering the chemical changes in the plant that initiate budding and flowering.  These are typically the plants that bloom as the days get longer in the spring and summer.

Short-day plants, as might be expected, do the opposite.  It’s the shortening of daylight and the lengthening of darkness that initiates bloom.  These are our fall blooming plants.

Plants that are not critically sensitive to the length of dark and light are called day-neutral plants.  While light plays a factor in day-neutral plants, other factors often play a bigger role in triggering the blooming cycle, such as the age of the plant.

An important thing to remember here is that even though the terms “long-day” and “short-day” make it sound like the length of the daylight is what is most important, it’s not.  What’s most important, what triggers the blooming process is the length of the darkness.  Darkness is what tells the plant when it’s time to bloom.

A Christmas cactus is a tropical plant, not a desert plant, and it’s a short-day plant – which means it needs long nights to initiate bloom.  In its natural habitat (the humid, coastal areas in Brazil) this plant typically blooms in May.  Remember that the seasons are opposite in the southern hemisphere, so May would be roughly equal to November in our northern hemisphere.

The Christmas cactus (genus Schlumbergera) needs a minimum of 12 hours of darkness each day for approximately 6 to 8 weeks before it will initiate bloom.  This requirement was taken care of for you before you first received your blooming plant at Christmastime, but if you want the plant to bloom again the next year, specifically at Christmas, you will need to do the job yourself.  Here’s how you do it:

After it blooms this holiday (if you just bought it or received it) care for it as you would most house plants.  Like the majority of house plants (note: there are always exceptions!) the Christmas cactus does just fine with moderate watering (not bone dry, not sopping wet), average humidity (not water dripping from the ceiling, not air so dry it hurts to breathe), and cool to moderate temperatures (60 to 70ish).

In other words, pretty much like we keep our homes in the winter.

In the spring, after temperatures consistently stay above 50 to 55 degrees at night, put your cactus outside, in an area where it receives morning sun (not hot afternoon sun) and let it spend the spring and summer season outside.  Like your other potted plants outdoors, be sure to water it when needed so it doesn’t dry out.

Now… here’s the tricky part.  Well, maybe not too tricky!  In the fall, when nighttime temperatures start to drop below that 55 degree mark, bring the cactus back inside.  Care for it as usual.  THEN… in mid-October, move it to a darker, cooler area of your house.  Put it in a room you don’t use much.  A second bathroom, or even a guest bedroom.  If the bedroom has windows that’s fine, because you’re not going in there turning the light on for hours every day so the cactus is only getting the natural light – and the natural darkness – from outside those windows.  (Of course, if the windows in that room face a blaring outside porch light then this won’t work.)

The main rule of thumb?  Indirect light for part of the day (such as naturally occurs during daylight hours), but keep it away from the artificial light after the sun goes down.  You are aiming for 12 hours or more of darkness.

As for watering, reduce the amount of water you give your cactus during this time, as you are inducing the cactus into a period of semi-dormancy and it doesn’t need a lot of water during dormancy.  Again, don’t let it go bone dry, but if the soil is a little dry to the touch each time before you give it a little water again, that is a good thing.  Think sips, not gulps.

In 6 to 8 weeks your cactus should start to show signs of budding.  This is when you can start to slowly integrate it back into the routine you had it in before you sent it into hibernation mode… slowly increasing the light exposure, slowly increasing the water schedule.

Your cactus will finally have gotten the rest it needs – no more insomnia – and to show it’s appreciation it should once again display it’s full bloom for you just in time for Christmas.

Happy Holidays everyone!