Answer: Japanese maples need a soil that is acidic, evenly moist, humusy and organic, yet well drained meaning not soggy or sopping wet. With a new plant, the problem could be related to poor rooting or planting incorrectly (for example too deeply or with encircling roots left intact), or it might be due to soil that is too wet or too dry, or it may be due to overfertilizing (this tree is not a heavy feeder and overfertilizing can cause root damage which will then show as a foliage problem) or some other soil incompatibility. It could also be caused by spring frost damage to the newly emerging leaves with the damage only becoming apparent now, or to accidental herbicide or chemical exposure.
In my experience, with a new tree it is more commonly a transplant/watering problem especially once the summer turns hot and the plant's water needs increase. Make sure the soil is slightly damp and water if needed to supplement rain. Dig into it with your finger and see. If it is still damp, do not water yet. When you water, water slowly and deeply and make sure it is soaking in thoroughly throughout the root area. After watering, wait a few hours and then dig down and see how far it soaked in, you want it to go about eight inches as this is a shallow rooted tree. It is better to water less often but deeply rather than a daily light sprinkling. Also, using an organic mulch in a flat layer over the root area will help maintain soil moisture, hold down weeds, and gradually feed the soil as it breaks down over time.
I hope this helps you trouble shoot. If none of the above sound plausible, youmight want to consult with your county extension and/or retailer since this is a new tree.
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