Mature Japanese maple turning green?

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Can you help with a question about our beloved ornamental Japanese maple?

We have a property in Memphis, TN (clay soil) with a mature Japanese maple that was well established when we bought in 2002. The tree used to have brilliant red leaves but its leaves now turn from red to green when the leaves unfold fully and when spring temperatures get above 80. The greening issue began perhaps seven years ago. We have other Japanese maples nearby (planted later in 2004, a different, more upright variety) that stay deep red all season.

The tree has grown at least 30% since 2002. The property was always shady but has become more so. There are large oaks to the northwest and northeast that have become more dense. One side of the Japanese maple gets direct sun between 8-noon, and the other side is in dense shade. The issue is the same on both the sun side and the shade side.

I don't believe the tree has returned to rootstock - the leaves are red when they first appear. I've gotten conflicting advice from tree services. Some say it's the natural result of aging. Some say it's getting too much sun; some say it's not getting enough sun. Some say fertilize it (which we have, with no result); some say it's getting too much food (so we skipped fertilizing, with no result). Some say it's a watering issue, others say its feeder roots are constrained by a nearby driveway (but this driveway is probably 10 feet from the trunk, and the dripline only overhangs the driveway by perhaps 18 inches).

The attached photos were taken this morning. The leaves are the same on both the sun side and the shade side. The leaves will be fully green within the month, I predict. Do you have any advice for me? Thank you!
 

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Not being able to see the tree in person I can only guess based on Maple tree characteristics. I think you have a combination of things going on here. Number one is the age of the tree. I bet the center of it is starting to degrade. Very common for Maples and won’t probably harm the tree any time soon. Second, because of the lack of direct daylong sunlight it probably is getting green to aid in photosynthesis. Red leaves are less effective at this. You could try trimming the tree back to give the root system a bit of strength advantage over the foliage but the tree is so nicely formed I wouldn’t touch it.
 
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Greetings, welcome to the Forums.

Increasing shade may be partly the cause of greening leaves in this case, but there may be other factors at play as well. Many red-leaved cultivars of Japanese Maples (Acer palmatum) will sometimes change color in Summer, even when grown in full sun. This is often called 'greening out' or 'bronzing out', and seems to be a reaction to mild heat stress. The weather, soil, other local conditions, as well as the age, establishment, and vigor of each particular tree can all affect this. Unless it becomes severe, there is no lasting harm. Still, growers continue to breed or find new cultivars that they hope will stay red under a wider variety of conditions. For example, Acer palmatum 'Wolff' (often sold as 'Emperor I') is usually considered to be an improvement over the older Acer palmatum 'Bloodgood', but I have seen A. palmatum 'Wolff' bronze out as well.
 
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No help with your problem, and I am not sure how true it is, but I remember being told that the red is an underlying colour that is always there, it is just that the green overpowers it and shades it out. They don't really change colour, just add more chlorophyll on top of the colour.
 

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