I have an oleander that I grow as a tree, like that :
I would like to try grafting other colors of oleander on some of the top branches, to make it a multicolor tree. I found videos online of how to proceed for the grafting itself but I have two remaining questions :
Briefly, your task will be to take a short piece of the new variety and join it to an existing branch. The cut ends will be somewhat bound together to maintain close contact and prevent drying out.
Choose a season when you are not expecting buffeting winds that could knock your grafts loose. Also bear in mind that you may want to enclose your graft with a balloon of clear plastic to maintain high humidity, so take into account the incidence of the sun on the grafted branch.
Since most of your fairly mature bush will be in flower-producing mode with short and woody branchlets this is exactly what you don't want, so to force the receiving branches into vegetative mode you might cut back a branch and force it to sprout out active green shoots suitable for graft. Both the stock and the scion should be in non-flowering mode; new, actively growing shoots.
Be sure to use a very sharp razor blade to cut your ends to make a good pairing surface on both sides.
