Cactus magic: Echinocactus polycephalus

We all need a bit of magic in our lives right now. Here's my contribution for today.

Take a cactus with seemingly gray spines:

Spray it with water:


Yes, it's the same cactus, Echinocactus polycephalus

Why do the spines turn red when wet? 

Because this is a magic cactus, and I have magic powers.

Just kidding. 

I really have no idea, but I'm sure somebody who's better at physics than me can explain this phenomenon.

Echinocactus polycephalus, known as cotton-top cactus (because of the woolly fruit) or Mojave mound, is native to the Mojave Desert and is found in places like the Mojave National PreserveAnza-Borrego Desert State ParkDeath Valley National Park. Its distribution in California actually quite widespread and includes the counties of Imperial, San Diego, Riverside, San Bernardino, Inyo and even the western edge of Kern County. 

My friend Jan Emming of Destination:Forever Ranch in northwestern Arizona has a great article about the conservation of Echinocactus polycephalus in Imperial County on his blog. I knew this cactus wasn't a speed demon, but I had no idea it took such a measured pace:
Cottontop barrels are among the slowest growing of all cacti, even when they are happy. “Rapid” growth could be said to be a plant that is putting out 3 to 5 new areoles per head, per year, which is maybe, possibly, 1/4″ of enlargement annually.
Echinocactus polycephalus is perfectly adapted to the arid environments it calls home. It's challenging in cultivation because its touchy about watering. I've potted my specimen in a very gritty mix that is about 70% inorganic (lava fines and pumice), and I'll keep it completely dry in the winter.

Here's a photo of a three-headed Echinocactus polycephalus at Pima Prickly Park in Tucson:

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  1. I do love it in the red version but then I expect it wouldn't appreciate having water thrown on it all the time, assuming that's what's required to keep it red. How long does it take to return to the white color?

  2. At least there isn't a need to repot them every other year.


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