Cacti trunk has shrunk

[cookiewise]

I bought two cacti from Ikea about 8 months ago. Both have been sitting in a south facing window in London, UK. They get a lot of light throughout the day but being London, the weather is very changeable (right now it is very blustery with not much consistent sun). However, until recently they seemed to be doing ok. One of the cacti is currently flowering and I am not too worried about it. However, the other one seems to have lost most of the mass of it's stem which was previously plump and swollen to the touch (it looks anorexic if a cacti can be described in such terms). I have not watered it until the day before yesterday as it was winter/early spring here and everything I have read advised that I don't water them until the growing season (Spring/Summer). I gave it a good watering the day before yesterday but it does not seem to have absorbed any water and I am wondering if lack of water was actually the problem? I did have to leave a window open overnight above the cacti as the room was painted and I needed to get rid of the fumes.

Photos attached. Perhaps someone can also identify these cacti whilst I am here? Thank you.

[adetheproducer]

This happened to my grafted sulcorebutia raushii, I thought it was simply a bit thirsty but water did not help and the hylocereus stock subsequently rotted taking the main scion with it albeit a month or two later. I saved offsets which I am still waiting to root but they seem fine. You might wish to remove and re-graft some of the offsets. Also keep an eye on tyour thread more responses will come from grafting experts which I am not.

[Steve Johnson]

You might wish to remove and re-graft some of the offsets.

Won't work on that moon cactus since the scion has no chlorophyll.

[cookiewise]

How do I remove a graft? Do I cut a chunk out of the stem? Also, what about the red graft? Do I need to take two separate specimens, one from the (green) trunk and one from the (red) graft? How do I put them together (I am a complete layperson when it comes to cacti, sorry!).

[Saxicola]

You might wish to remove and re-graft some of the offsets.

Won't work on that moon cactus since the scion has no chlorophyll.

No reason why that wouldn't work. He wasn't saying remove the offsets and root them. He said to regraft them. Though the OP is new enough to this that jumping right into grafting might be too much too soon.

[greenknight]

You need to take it out of the pot and see if the roots have rotted. It's possible that the problem is it's potted in peat which is dried out and resisting absorbing water. If that's the problem, the solution would be to submerge the pot in lukewarm water until it does get soaked. If that is it, after it recovers you should remove the old soil from the roots and re-pot it in a better mix.

If the roots are rotten, cut off all the rot. Even if that means removing all the roots - it will last longer without roots than with rot. You could try re-rooting it , too - I've never heard of anyone doing that with a grafted cactus, but nothing to lose. You could take off some offsets and graft them, and still try to re-root the old plant.

The red graft has produced a whole cluster of offsets, each one of them could be grafted onto a separate stock plant to create a new "moon cactus" - that's how these things are produced. You'd need to obtain another plant to use for grafting stock (the green part) for each one.

If you want to try grafting, this is a good opportunity - you've got nothing to lose, it's dying as it is. Take a look at the "Grafting" forum, there are instructions there on several different methods - see if it's something you'd like to try.

[Steve Johnson]

You might wish to remove and re-graft some of the offsets.

Won't work on that moon cactus since the scion has no chlorophyll.

No reason why that wouldn't work. He wasn't saying remove the offsets and root them. He said to regraft them. Though the OP is new enough to this that jumping right into grafting might be too much too soon.

Should've looked before I leaped -- sorry about that!