I have tried growing rebutias before, and failed because the plants lacked vigor and grew slowly. Would they do better if I flat-grafted it onto a columnar Echinopsis, to increase vigor? Are there any better rootstocks? Should I use a columnar type as a rootstock?
In my opinion, bigger but not better.
I find it beautiful grafts between succulents, as much as I find weak results. The grafted plants have beautiful color effects and forms, but generally do not have a long life. At least in my experience.
A columnar type, such as basic, not very high (proportionally to diameter of fust), it may be a good solution because the lymph veins are straight and pointing upward, hence prone to channel nutrients to the graft.
It is known that this type of inclusion promotes the growth of the graft, which gets bigger faster but weakens. If the graft is not perfect, very soon they will develop rot. Otherwise the weakened plant will be easy prey to diseases.
As note, I prefer to grow succulents in a natural way. They take time to grow and I keep the patience to wait them to grow. Called Zen :-]