In article , Robin Graham
writes
I have an 18" tall ribbed cactus which was being eaten away about 4" from
the top and I was afraid that the top part would simply die. So I cut the
top off above the bad bit and cut the bad bit off the main stem and tried to
graft the top onto the bottom, if you see what I mean.

I held the top bit hard to the bottom bit with a weight, hoping it would
graft itself and grow together. Unfortunately, someone hit the thing and
knocked off the top bit and I now see that the cut ends, top and bottom,
have simply calloused over without trying to grow together.

What should I do to make this work?

You have to get a very good match between the two bits, so that there is
no air between them, and to hold them together very firmly. If you
wanted to try again, you would need to cut both ends again.

I'd suggest abandoning ideas of grafting, and simply grow on both parts
separately. If you place the top on top of damp cactus compost, it
should root and within a few years get back to 18 inches; meanwhile, the
stump will send up one or more offshoots from the top.

What on earth was eating it?

--
Kay
"Do not insult the crocodile until you have crossed the river"