Recently I put a plumeria into the ground for the first time. (Imagine my sadness when I heard la NiƱa will return in the fall
) I mixed in some perlite into my soil, just in case. It is nice soil but I, too worried about proper drainage. I loosened up the soil bigger than the pot and just planted the plant, soil and all into the hole. I raised it up some so that the water can drain away. So basically the little tree is growing on a mound. It's been in the ground for about 6 weeks. So far so good. It did fine even during our heavy rains. I fertilize it frequently. It is growing many leaves now.