“I recently bought a house in Long Island, NY, and found a 2-foot tall Japanese maple tree (I believe it is a Red Emperor Maple) growing under a much larger tree. The maple apparently sprouted naturally. I would like to transplant it to a more open space. When is the best time to transplant the tree? See pictures of the tree and proposed a new planting spot. This open location will get much more sun, will that be a problem? Any advice on transplanting (size of root ball; conditioning soil) are welcome. From my reading it seems that it is best to transplant the tree before the first frost in autumn, the root ball should be the diameter of the drip line, and the new soil should be well-draining and mixed with lots of organic matter.” Question from Ron of New York, New York
Answer: The tree looks healthy, and the planting spot looks just fine, but seedling trees like this little Japanese maple (Acer palmatum, USDA Hardiness Zones 5-8) have one flaw relative to nursery stock. Their fine, spreading roots are not as dense as those of potted trees, so they do not transplant as well. There is one way to increase root density for better establishment, root pruning. If you prune the roots in fall, the tree will be ready to plant before it leafs out in spring. Here’s how.
How to Root Prune a Tree Before Transplant
You will need a sharp flat spade (King of Spades is best), gloves, and probably some pruning shears to cut away the ivy. Trim the ivy away, clear the area to begin digging. Shoot for a root ball with a circumference of 8-10 inches around the tree. Using your sharp spade, make clean, slightly angeled cuts down to the full length of the spade. You may run into competing tree roots from the larger tree. Cut around them as best you can. Once you have made the cuts all around, leave the tree until spring. Where you made the cuts, new feeder roots will grow over the winter to help the tree become well established when you move it in spring, so you don’t need to cut along the drip line.
In spring, pull away the mulch, and dig a hole that is several inches beyond the height and width of your tree’s root ball. Break up some of the backfill to help plant the tree, and reserve the rest to fill in the hole you will create by digging up the tree.
Next, gently dig around your maple along the lines and cuts you made in fall. You will have to dig a bit beyond the cuts to get any roots that you missed towards the bottom. You should see new root growth along the cuts. Wrap the root ball in plastic or burlap to keep it together. If it breaks apart a little, your tree should still make it. From there, I recommend that you click on this link to follow Russell Stafford’s guidelines for planting a new tree.
As to the variety of your Asian-native Japanese maple, it is difficult to say. These maples seed in from planted landscape specimens, and the seedlings are not necessarily true to parent. With that said, it should still be a fine tree. They can reach a maximum height of 25 feet, so it will provide some shade in your front yard.
Happy tree planting!
Black Gold Horticulturist