It is safe to use any of the Osmocote formulas on potted trees and shrubs but do not over fertilize Japanese maples. I use one tablespoon of Osmocote per year on my potted Japanese maples because I do not want to encourage too much new growth - I like to keep my Japanese maples in containers for 7 to 10 years before repotting them. If you want to encourage faster growth, add 2 tablespoons of Osmocote, but no more. I also protect my potted maples from the afternoon sun and feel the soil with my finger before watering. The goal is to keep the soil just slightly moist but not wet and to make sure that the water drains freely from the holes in the pot. One of my potted maples is not a 10 foot tree growing in a large pot and you just reminded me that now that I see signs of new foliage, I better get outside and fertilize my own potted plants. Keep growing, Marianne Binetti