It's not a plant I'm familiar with but one option if you want them to branch early is to remove the growing point (which I assume is what Daisy meant by "encouraging" it). That will typically cause a plant to branch. I hesitate to suggest it since I don't know the plant but I did check one web site that said it was OK to do this with Tabebuia. If you don't want to risk it with all of them, just try one and if it branches then you'd know it works with them.
