Japanese maples (Acer palmatum) are a small ornamental tree much prized in the landscape. Several cultivars have been developed based on native species, and the ones used in landscaping are chosen for their distinctive colors-bright green, dark red, or reddish purple.
Red Trees That Turn Green
It can come as something of a shock, then, when a tree we picked because of its color begins to change to another color over time. Japanese maples are one such tree in which this frequently happens. Usually, it is a red or purple cultivar that gradually begins to transform into a green tree, and this can be disappointing if you've selected the tree specifically because of its color.
The Biology of Color Change in Japanese Maples
To understand how a tree's color can shift, you need to understand how horticulturists obtain those unusual colors in the first place.
All true Japanese maples are variants of the sturdy green Acer palmatum. If you happen to have one of these pure species types, there's almost no chance that your tree will change colors. To produce tree cultivars with unusual colors, horticulturists may begin with the original species root-stock, then graft on branches with different characteristics. (There are other ways in which tree cultivars can be created, but this is a common technique used for Japanese maples.)
Many tree cultivars originally start as a genetic accident or an aberration that appeared on an otherwise normal tree. If that aberration was appealing, horticulturists may then seek to propagate that "mistake" and create a whole line of trees that duplicate that unusual characteristic. Many trees with variegated leaves or unique leaf colors or unusual fruits began their lives as "sports," or genetic mistakes that were then deliberately cultivated through different methods, including grafting new branches onto hardy rootstocks. In the case of red or purple Japanese maples, branches from trees with desired colors are grafted onto hardier rootstocks that are more durable in the landscape.
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.
How to Correct or Prevent the Problem
You may be able to catch the problem before it becomes severe if you 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.
Should your tree lose all its grafted branches-as sometimes happens when Japanese maples are planted in the northern limits of their hardiness zone range-your tree cannot be returned to its red color. All branches that sucker up from below the graft will be green in color. You can either learn to love the green Japanese maple or replace the tree.