There's many way to propagate bougainvillea you know on RU-vid, most of them is small cuttings, very easy to grow. But you might not know how to do for the large cuttings, here is other way, my way. I hope you do it successful.
PS. Some how I didn't have the video when I paint on the top of them (as you see at minutes 6:48). I'm sorry about that. It is the paint I put on top to protect the logs from fungus and also keep the logs from drying.
Best regards
7 сен 2020