I bought this cactus, Cleistocactus coladmononis a couple of years ago from Hampton Court Flower Show. I have slowly been falling in love with cactii and this one was one of the first to attach itself to me.
You might be able to tell quite quickly what the issue is....
This cactus has grown really well from how it was when I first brought it home. I have repotted it into special cactus compost and I have looked after it. I feed it every couple of weeks in the growing season and keep it fairly dry over the winter.
It has rewarded me by starting to grow new limbs. I love how they flow and look almost soft (believe me they are not, the spines are quite wicked).
The other day I knocked it off the windowsill. The limb split open and it bled, it did, it bled. I swore, a lot. I firstly thought maybe I should cut the poorly limb off. Then I googled to see whether it could heal. To be honest I think the general answer was no it will not heal or at best, not very well. However never one to just believe what I read no matter how much more the author knows than I, I decided to bandage it up with grafting tape.
Of course I am irritated with myself, not the plant, the plant is the innocent victim of my clumsiness. Whether this will work or not I am not holding out much hope, but I felt a little less guilty by at least trying to rescue it. I will let you know how it gets on.
