What is causing my pencil cactus branches to get soft?

Question

I have a good size 3ft tall x 2. 5ft indoor pencil cactus given to me a few years ago. It has been healthy and growing – loves the sunny location I’ve had it at for 2 yrs. Scenario, the top smaller branches started to get soft and parts were a bit droopy. I have inspected closely, thought perhaps some tan crusty spots/lines were scale? (1/16 inch wide – inch long) I did a complete careful treating with alchohol and Q-tips but then cut off a few and they were not oozing sap. . so cut off a few more, and some DID ooze sap. A few dead pieces, . . so I pruned it very moderatly; took off the branches instead  of treating them. Then two weeks later, (getting more concerned) I decided it was time to repot anyway (3+yrs in same soil) . . . and only way to inspect for root rot. I found healthy off white hard roots. . . I repotted in combo Cactus/Reg miracle grow soil. . (mostly cactus) and did not water for a few days. Then moderately watered. I see zero improvement in 2 weeks. . I am torn about this as; my friend who gave me this plant insists that it needs more water than I told her I give it. (No online resources say it needs lots of watering) I watered it religiously every 7-10 days lightly, , less in winter, . . and twice in summer it went outside and got a full flush. (I do not leave it outside – have LOTS of indoor plants must be careful about bringing in pests) Use organic products mostly. Fertilized 3 times a year. Room has skylights and a window near the top edges of the plant. IT is on a table next to this near ceiling flip out window.  It got really cold about 60 days ago when I forgot to crank it shut; got to 30 outside. So, . could one cold night by a slightly open window damage it this much? Am I watering too little, ? 2. 5 ish  cups at the most every week. Is in a 12 in pot – base stem is solid 1. 75 in. in diameter) 3ft tall now pruned. Major branches are quarter in. diameter. This is bumming me out can’t find a thing online to help me know what is causing this soft limpy branch thing. . . HELP! I want to be patient, but if there is something anyone sees as to try. .

Answer 1

Yes, one cold night could do this. It only needs an hour or so of exposure to freezing temps to do damage. The outermost branches would be affected the most and first. If it is cold damaged, and the symptoms would fit, there is not much you can do for the cold damaged areas. What basically happens is that the plant cells get punctured by the ice crystals that form and they literally leak to death, which is why it might look fine in the morning but then progressively gets worse as time passes and seems to deflate. there is no way to fix the holes in the cell walls.

Fortunately, it can regrow after cold damaged as long as part of the plant went unscathed.

As to watering, with succulents, it is best that you check on a schedule rather than watering on a schedule. Only water if the top of the soil is dry and water until the water comes through the bottom of the container. Watering succulents on a scheduled is to invite root rot, though it sounds like yours is not affected by this at this time.

Just as a precaution, consider treating the plant with a fungicide. A fungus could also give the plant the symptoms you describe.