Ahhh, the Christmas cactus or, as my friend's mother-in-law calls it, the Hanukkah plant.  Also known as the crab cactus or Thanksgiving cactus, no matter what you call it, you have likely acquired at least one of these lushly flowering winter perennials through the years.  No surprise there...  With vibrant red, hot pink, purple-burgundy, and even orange blooms, the Christmas cactus is perfectly timed to brighten up the dark dreariness of the winter season.  While all is merry and bright while your Christmas cactus is in bloom, what do you do when your plant turns into a drooping, flower-less vision of sadness?  Fear not.  Instead, keep reading to learn exactly…