Certified GKH Gardening Expert
Worm castings, on their own, are not a fertilizer. They are an amendment to loosen up compacted soils, and improve texture. I love keeping worm castings around and wouldn't imagine getting a refund. They are very useful, though they are not a fertilizer.
As far as fertilization goes- This article will help: https://www.gardeningknowhow.com/ornamental/flowers/plumeria/how-to-fertilize-plumeria.htm