The Japanese maple tree (Acer palmatum) is a popular garden accent, grown both in the ground and in containers. According to Master Gardeners at Washington State University, the Japanese maple is not a heavy feeder and, in fact, may lose some of its color if over-fertilized. What to feed the tree, and how often, seems to be a hotly debated topic in gardening circles (UBC). As long as the tree isn't over-fertilized, it should thrive in your USDA zone 6 to 9 container garden.
Water the Japanese maple tree until the water runs from the bottom of the pot.
Sprinkle the fertilizer on the soil, at half the rate suggested on the label, not allowing it to touch the tree's bark.
Use the trowel to scratch the fertilizer into the top 2 inches of soil.
Water the Japanese maple again, just enough to wet the top 4 inches of soil.
Withhold fertilizer in August. A late-season burst of growth may not harden in time to protect itself from early frosts, according to Todd Boland, a research horticulturist. Begin fertilizing again in spring, as soon as you notice new growth.