Question
Hi there!

I relocated my 3 smaller Christmas Cacti to my room about a week ago (I work thirds and like my room on the chilly side, so it's always about 60* and dark), and now one of the 'younger' ones is sprouting air roots around the latest segment. Any idea why it's doing this? The other two aren't, nor is my big one in the other room. This fall it sent out a ton of new growth right along with the other 3, so I thought I was doing well with it.

Also, I always forget when you're supposed to fertilize. Do I do it prior to blossoms forming, during the blossoming period, or in the spring after the blossoms have stopped? I usually add a bit of fertilizer when it's doing alot of new growth, but with blossoms I'm never sure.

If it's any relation, I'm in Ohio, but the plants are always indoors. There's a fan in the room for both sound for me and air flow for the plants, and the temps are pretty much about 55* at the coldest and 65* at the warmest right now. They're on the table with my orchid, so they're getting a little bit of the light it gets (a table-top gooseneck lamp angled directly over the orchid), but otherwise pretty much dark from 2pm to 7am.

Answer
Dear Amanda,

Sorry for the delay in responding.  I didn't get your original e-mail.  As for your cactus with some air roots, there are a couple of possibilities, and neither is worrisome.  

First, Christmas cactus are hybrids of epiphytes.  That is, in their native habituate which is tropical jungle, they grow in trees and sometimes on rocks and and get some of their moisture from their aerial roots.  You don't normally this this with Christmas and Thanksgiving cacti, tho I don' think it is out of the question.  It is more often in in another family, which are the Easter cacti, called Rhipsalidopsis gaertneri. So are all your cuttings from the same plant?

Secondly, it may be that this plant is a Schlumbergera (Christmas or Thanksgiving cactus) isn't getting enough moisture and so is sending out air roots to try to get more.  I think this is less likely and my first explanation is more likely.  Either way, it will do fine with your other jungle cacti.

As for feeding, Epiphytes such as Schlumbergeras and Rhipsalidopsis need acidic soil with pH at about 5.5 to 6.2 or so. Hence, if alkaline tap water is used to irrigate these plants, it is wise to acidify it with about a teaspoonful of vinegar to a gallon. Many very successful growers dispose of their stale tea in the Christmas Cactus soil, and they swear by it. No doubt the tannic acid does the job. But nothing beats an occasional test with an acidity meter, or a litmus paper checkup, and pH adjustment as required with nitric acid.

In a soilless mix, Some growers of epiphytes recommend soluble fertilizer formulations of #15-30-15# once or twice a year. I recommend a dose, following package directions, once after each of the two short dormancy periods following the two main flushes of bloom in Oct/diluted and Mar/May. For the rest of the growing periods, May to September, a 9-9-26 formulation, diluted to less than package recommendations, to use at every second watering or so. The high proportion of potassium #26# has been responsible for deepening the colors of the flowers and for inducing a greater number of branches to bloom as well as more twin and triplet blooms per branch.

Your temps and light seem to be on target.

I hope this helps and if you have any other questions please don't hesitate to write.

Good luck,

Maureen