Help with cactus

[kwl11]

Hi! So I’m trying to save the top half of a very small cactus. I’m not very optimistic because I had to cut off a large portion, and it’s not an easily-propagatable part (like a pad). The bottom half died because it had been planted in peat soil, and it never crossed my mind that the seller could have used the wrong kind of soil. I think the bottom has scabbed over, but I’m worried because some of the areoles are turning grey. The number of grey areoles has increased since I removed the cactus bottom (about two weeks ago) but the other half of the cactus looks perfectly green. The cactus overall and grey areoles are surprisingly firm, and I cut off a few of the grey spots and the inside still looks green (not rotted).

I have a couple questions about this:
1. Is this greying is normal/is it part of the healing process?
2. Will the cactus recover from this?
3. If it can recover, how long will it take for the cactus to put out roots? (How long should I wait before calling it quits?)
4. How should I care for it? Should I water it more frequently than a healthy cactus? Should I set it on top of soil?

Thanks in advance!

[tumamoc]

It looks like normal callousing to me, considering the trauma. I would partially bury it in some dry, gritty soil. If kept in warm conditions, the first root growth could be in a couple of weeks or a couple months. It's gonna do what it's gonna do. I don't know your location, but approaching the cold weather seasons, you might try to root it indoors where there is decent light. If you pull on it slightly and there is resistance, that's a good sign of root growth. I usually have little patience for this, so I pull it out of the soil about once a week to see if there are any root nubs or filaments. There's no sense watering the plant until the roots appear, but intermittent moisture won't hurt if you want to give it an occasional splash. Once rooted, watering should be the same as your other healthy plants.

[kwl11]

Sounds good. I keep the cactus inside because I live in a really humid area.
Thanks for the help!