Whether your small Japanese maple trees need fertilization is a matter of contention among horticulturalists. According to Ron Smith of North Dakota State University, Japanese maples do not need fertilization as long as they are grown in fertile, loamy soil that drains well. But other sources, like the University of Minnesota, suggest fertilizing small maple trees. Light to moderate fertilization likely will not harm your Japanese maple and may in fact help.
Select a balanced, slow release granular dry fertilizer for the soil around your Japanese maple. A balanced fertilizer has N-P-H numbers--the percentage of nitrogen, phosphorous and potassium in the fertilizer--with equal numbers in all three positions, like 10-10-10.
Consult the packaging for fertilizer quantities. Different fertilizers may require differing quantities for similar results. For example, you would apply more 10-10-10 fertilizer than you would 20-20-20.
Scatter the recommended amount of fertilizer on the root zone in the spring. Be careful not to allow the fertilizer to come into contact with the tree trunk, which some fertilizers can damage.
Water the fertilizer in with 1 or 2 inches of water. Do not apply too much water or you risk having the fertilizer dissipated in runoff.
Consider mulching after fertilization to help retain soil moisture and protect the roots of your tree from both winter cold and summer heat. Mulch can also protect your tree from lawn mower and weed cutter damage.