I have been given what was a standard Oleander, which is now a good 60 cm taller than it should be. My question is, how hard can I prune it? Not only is it too tall, it must have been close to a wall because most of its branches are on one side, which makes it difficult to keep it upright. I have repotted it.
Rejuvenating prunes should be done over a period of time instead of one big chopping session.
This link will help you.