What time of year is good to plant a Japanese Maple Tree?
However, maples, including Japanese maples, can be transplanted readily in either fall or spring, so go right ahead.
Be sure to dig a hole twice as wide as the root ball and slightly shallower that it is deep. Chop up the backfill as finely as you can and place it firmly back around the root ball.
Give the tree a good drink of water, put 2-3" of mulch on top (but not up against the tree trunk), and enjoy its leafing out next spring.