Answer: Japanese maples need an acid soil that is evenly moist but also well drained, meaning not sopping wet. They do best in a soil that is rich in humus rather than in heavy clay. Clay tends to hold moisture and exclude air, so it is possible that it has been overwatered.
Overfertilizing with a foliar feed or at the root zone could also show up as discolored foliage or browning.
Transplanting is also very stressful and it takes some time for the plant to grow new roots and become established; very hot weather could also stress the plant and show up as browned foliage.
You might try checking the soil with your fingers before watering, just to make sure that you need to water. Also, put several inches of organic mulch such as shredded bark around the root zone of the tree to help keep the soil cool and conserve moisture during the hotter and drier summer, but do not allow it to touch the bark. Apart from that, there is not much to do but wait and see if it comes through.
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