I do think using Osmocote is a good idea for your transplanted Japanese maples that you put into pots but instead of putting the fertilizer pellets into holes, mix it into the surrounding soil in a circle around the new roots that goes out about five inches on all sides. Just one tablespoon of Osmocote Plus for a plant that was in a gallon container is my recommendation. I would wait until mid spring when you see the trees leafing out before applying the fertilizer. A mulch on top of the roots in the summer and adequate water are also important to insure the newly grafted trees survive and build a good root system the first summer in the ground. Congrats on your successful graft of Japanese Maples - sounds like you enjoy a green thumb! Keep growing, Marianne Binetti