Cactus Problem...

[Kamisama420]

Hi guys,

Some of you may remember me for my mint, which I believe is doing fine by the way, I'll update you on that soon, but right now my problem lies in my new acquisition: a cactus.

From what I could find on the net, this is a grafted Moon Cactus. I bought it alongside another small one, as you can see in this picture.

Now I made a rookie mistake, which was to put it on my window sill in the middle of summer, which blasted the cactus with direct sunlight. Apparently, cacti don't like too much sunlight. My idea was that cactus = desert = sunlight 365 days a year, but I obviously I was wrong.
The side that was facing the window turned white. I removed it from the sill and put it further where there isn't that much sunlight. The other two sides are now turning yellow, and I suspect one corner to be infected or rotting. See for yourself:

Side that was facing the window:

Side that could be rotting:

Third side:

The question is: how do I fix it? Is it doomed already?

All advice is very welcome.
Thank you.

Kami

 

[Brandie]

What soil are you using? Also, how often do you water it? I def don't believe sunlight is the root problem.

 

[Brandie]

And it's def rotting. Take it out of the soil and change it to a sandy mix. But let the whole plant dry out for a few days before repotting, pregerably in a larger pot. Same for Avocado. Both need excellent drainage.

 

[Kamisama420]

I bought it as is from a plant nursery, pot an all. I don't know what soil they used, but it's a bit hard for me to believe they don't know what they're doing. It was a healthy green and now is rotting less than two weeks after I bought it.
I have not watered it yet because I was told that a little water every other week or so was enough.

Any thoughts?

 

[Brandie]

So what might have happened is that at some point it got an abrasion or cut and got infected. Could be bacterial or fungal. I would take it back to nursery.

 

[Brandie]

You could also try putting it in a larger container with good drainage and cactus soil. See how it does then. Good luck!

 

[Beth_B]

Well I can't fault your logic, and it's not being drowned...but I agree with Brandie; take it back to the store. They probably have some sort of guarantee. Also repotting it surely wouldn't hurt; that way you can see what the roots look like.

 

[Corzhens]

I can liken that cactus to our dragon fruit especially because it has the same size and looks of the limb (or stem). When the green skin turns yellowish that means the stem has reached the end of maturity and it will die. However, there are times that the yellowish color is caused by excessive sunlight maybe (not sure on this) and it becomes green again which means it is not that mature yet and the discoloration is artificial.

But in the case of your cactus, the rotten part is quite big and sorry to say but it is discouraging. I hope I am wrong.