There are a number of reasons you might want to transplant a Japanese maple. The most common is when you want to establish a new tree from nursery stock outdoors. In some cases, your existing Japanese maple might have outgrown its location or not be growing in an ideal location. If you grow Japanese maple in pots, you should re-pot the tree every two years to keep it from becoming root bound.
Existing Outdoor Trees
Select a good new location for your Japanese maple. Japanese maples do better in locations that are partly shaded and require soil that drains well.
Dig a hole to receive your tree. In general, dig the hole as many feet wide and deep as the thickness of the trunk is in inches. For example, if the trunk is 3 inches thick, dig a hole 3 feet wide and deep.
Dig a trench around your existing tree about 3 inches narrower than the hole in which you will place the tree. For example, if your new location has a 3 foot hole, dig a circular trench about 2 1/2 feet in circumference. Sever any roots growing wider than 2 1/2 feet. This will ensure that the tree will fit properly in the new location. The roots will grow back in the new location.
Dig down to below the bottom of the roots, if possible. If your Japanese maple's roots have gone deep, dig down to around 6 inches above the bottom of the hole in the new location. For example, if your new hole is 3 feet, dig down 2 1/2 feet. Sever any roots that grow deeper than 2 1/2 feet.
Pry the tree out of the existing location with a shovel. For particularly well rooted trees, you may need a couple of shovels to free the tree from the ground.
Lift the tree out of the existing location and move it to the new hole. Depending on the size of your tree, this may require several people.
Place the tree in the new hole. Check the level of the trunk. If the trunk is too far below the surface of the surrounding ground, lift the tree out and add soil to the bottom of the hole to raise the tree. If the roots stick up above the ground, remove a enough soil to allow the tree to sit deeper in the hole.
Backfill the sides of the hole once the base tree level is to your liking. Wiggle the tree as you fill the hole to ensure that there are no air pockets around the roots.
Water the tree thoroughly. Water the tree every few days to make sure it gets enough water as the new root system establishes.
Select a good location that has partial sun and partial shade. Dig a hole several inches larger than the pot in which your young tree is growing.
Remove the tree from the pot. If the tree is root bound in the pot, one easy way to get it out is to cut the pot off the roots with a utility knife.
Place the tree in the hole and look at where the trunk level. If the root ball is sitting too deep in the hole, add some soil to raise it. If the root ball sits above the level of the adjacent soil, dig out a bit more soil until it is level.
Back fill the sides of the hole to secure the tree. Wiggle the tree a bit to ensure that soil fills as much of the sides and bottom of the hole.
Water your newly planted young tree thoroughly. Water the tree every two or three days for several weeks until the root system is better established.
Potted Japanese Maples
Re-pot or trim the roots of your potted Japanese maples every two years. This will ensure that the root system has adequate air space and will prevent the tree from becoming root bound.
Loosen the sides of the root ball if they are pressing against the sides of the pot. For larger pots, a small hand shovel works well. For smaller pots, such as bonsai, use a kitchen knife.
Turn the tree and pot upside down, if the tree is small enough. The tree should slide out. For larger potted maples, lift the tree up by its trunk while pressing down on the pot. If your pot is a heavy ceramic pot, it should slide off easily. You may need to hit lighter plastic pots around the rim to get them to separate from the roots.
Trim off about one-third to one-half of the roots with sharp pruning shears if you are planning on putting the tree back in its original pot. If you are re-potting the tree in a larger pot, trim off about a quarter of the roots.
Loosen the roots and remove as much of the original soil as possible.
Fan the roots out and place the tree in the pot. Begin filling the pot with soil that drains very well. Use your hands to spread the soil around the lower parts of the roots.
Continue filling the pot until it is full. Water your tree thoroughly. Water the tree every two or three days for a month or so until the new root system establishes.