How's their soil? It should be very well-draining. And indoors, they're not going to get very much light, even with a nice window. You have to be very careful about the watering. Do some searches on good soil mixes and then compare to yours, and maybe take a look at how the roots are doing. If it's rot, you'll have to operate (slice off the rotten portion), leave the healthy growth, let the end you've cut callous over for a few days, and then place it in proper soil and let it develop healthy roots again.

I'm no expert, but it looks to me like that red one is rotting inside the top part, not the stem! That's bad..I think you'll probably just have to get rid of that one because that red part is grafted onto the stem of another plant, so the top part won't regrow if you cut it off. The yellow one does look like its stalk is drying out..possibly because the roots have rotten? How often would you say you've been watering it? The number one cause of death for cacti and succulents is overwatering

I'd say your best bet would be to re-pot it in a fast-draining, porous soil mix. Like Teatree said, you can search for some good soil mixes or just make a simple mix of 50% perlite and 50% potting soil. That won't be the BEST mix for, but the plant will be happy and dry. When you repot it, rub all of the old soil off of the roots and take note of what color the roots are..they should be fairly white, not brown or black (rotten).

One more thing: the pot you plant it in should be able to breathe as well; regular ole terra cotta is the best and will only cost you about 75 cents. Don't water it for a week or so after you re-pot it, and then only water it every few weeks when the soil has completely dried out.

Good luck!

i think thats just the remains of the chlorophyl from the graft, couchpotato89, i could be wrong, a few more pics might help.

I think the orange one, on the left does look sunburned, the cactus on top usually burns too tho, i see no sign of that...

still the advice is the same, unpot, examine, treat, dry, repot and hope for the best, the good news is, the rootstocks there are tough, i bet atleast one of them survives, you might be surprized what a nice plant that can make...

Well, I have found that the scion (the bottom part) is a short lived section of Hylocereus undatus. What you have is a desert cactus grafted onto a jungle cactus. The top plants (Gymnocalycium mihanovichii) lack chlorophyll and cannot make food for themselves. So you have to keep it watered well enough to support the Hylocereus.

The red one may be reverting and making chlorophyll. In that case, with a little time and luck, you might de-graft it and have a long lived plant on its own roots. The yellow ones don't often revert.

I see that red one with "remains of chlorophyl" in it alot in the big box stores, never have really understood why.

Its always just olive to dark green, with some purple blush sometimes, just like when they grow on their own roots.

also the bottom plant in a graft is called the stock, the top is the scion.

Wow; I didn't know that the scion could revert and grow on its own! Normally I don't see any of these "moon cacti" that I like, but I'll start looking for that dark red color in the future.

Good luck saving them, Spikey9!

I always avoid these things, as bad as those cacti seen with glued on flowers.
If I had one Id cut the top off for the compost and hope the scion grows pups near the cut!

here is my experience w/these plants. My son bought me on Mother's day in school in 2011. Personally I don't really like them. i replanted right away in gritty mix,cleaned all the roots. it survived more than a year but finally died last September. Maybe i didn't water it enough to keep roots. but I'm kind of proud it lived more than a year. I heard its very hard to keep them alive

Inna

Inna

Sorry, but these just look too fake to me, I don't think they are meant to live long, not my cup of tea. Sort of like those Phalaenopsis orchids that are dyed blue, just not natural. Indeed, the dragonfruit scion appeals to me more.

Christopher

Im with you Kris!