Japanese Maple feeding
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Japanese Maples are beautiful trees!
For fertilizing, we recommend you do a soil test to look at the nutrient availability in your soil before making specific recommendations. Japanese Maples don't usually need additional fertilizer as long as the soil organic matter levels are good- which can be determined by a soil test.
CSU Soil testing: http://www.soiltestinglab.colostate.edu/
Here are some publications with detailed information on their needs, management recommendations, and troubleshooting issues: