Yes, I have used Osmocote myself for just this purpose. First dig a hole and mix the tablespoon of Osmocote into the surrounding soil. Add the seedling maple and in early summer once the weather is warm and the seedling is putting on active new growth the soil temp will activate the fertilizer inside the little pellets and through osmosis the fertilizer will be released slowly to the growing maple. This way you won\'t burn the tips of the seedling leaves by applying too much fertilizer. Keep growing, Marianne Binetti