Answer: You can dig and transplant a Japanese maple with a good degree of success if you wait until December when it is dormant. If you try to move it now, after it has leafed out, it will be severely stressed and it may not recover. In the winter it will be dormant and the ground will be cool and wet so the transition should be easy.
The roots of a Japanese maple generally extend out past the longest branches but if you begin your digging just inside the longest branches the only roots you'll be cutting off will be the smallest ones that are the easiest to replace. Depending upon how long the tree has been in the ground, you may find the majority of the root mass in the top 12" of soil. So your goal is to begin digging at the ends of the branches. Explore with your shovel to see where the largest roots are and try not to sever them. Dig under and around those major roots to remove excess soil (to make the move easier). You and a friend can probably pry it out of the ground without too much trouble. When you replant, make sure that it is resting at the same soil level as it was growing before and be sure to water it in well to help settle the soil.
Hope the move is successful!
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