I have a Mikazuki Japanese Maple planted in a protected corner of my south facing backyard in Toronto. The tree leafs out red in the spring and gradually turns a variegated green over the course of the summer. Recently I noticed one branch sprouting bright red leaves (please see attached photo). I wondered what would cause this and if I should be concerned that the tree is undergoing some stress? Is it reverting? The soil is regularly amended with good leaf compost and the garden is well watered. Thank you in advance for your suggestions.
Thank you for contacting Toronto Master Gardeners.
Looking at the photo it looks like the branch in question has a very different growth pattern than all the other branches and the bark looks like it is a bit different. The branch looks like it grows straight from the base of the plant. The bottom of the plant does not show in the picture, but I suspect this branch is growing from the root stock below the graft. Many ornamental Japanese maples are grafted so have a root stock of a hardy, less ornamental Japanese maple with the hybrid grafted on top. You can often see where a graft is by looking for scars and a thickened area on the trunk. It is not unusual for the root stock to send up branches that look different than the desired hybrid.
If the branch does come from the base root stock then it should be removed right down to where it attaches to the trunk. If root stock branches are allowed to grow they will take over and the ornamental branches will not thrive.
If this is not the case please send some photos with close ups showing the trunk and leaves in question.