Asked May 15, 2021, 9:56 AM EDT
Wake County North Carolina
After a bit of research, which I noticed had many suggestions, I believe it has to be that these maples are grafted from the more common green Acer palmatum.
On a Japanese maple, harsh weather or other factors sometimes kill off the grafted branches, which are usually attached to the rootstock near ground level. When this happens, the new branches that sprout ("sucker") up from the ground will have the genetic makeup of the original rootstock—which will be green, rather than red or purple. Or, it's possible that new branches may sucker up from below the graft in addition to the red-leaved branches that are grafted onto the tree. In this case, you may suddenly find yourself with a tree that has both green- and red-leaved branches.
You can periodically inspect the tree and pinch off any small branches that appear below the graft line on the tree. This may result in a tree that's somewhat asymmetrical for a time, but steady work getting rid of the green branches sprouting from below the graft line will eventually return the tree to its desired color. Japanese maples, though, do not tolerate heavy pruning, and because this is a slow-growing tree, it takes patience over time to allow the tree to form a natural shape.
I hope this helps! Please let us know if you have any other questions.