Answer: Since it is a new plant and this is the heat of summer I would think it is related to that, the tree will need a few years to become fully rooted and well established. Keep the soil moist as you have been doing but be careful not to overwater it, the soil should be like a wrung out sponge, not sopping wet. A layer of organic mulch several inches thick (two to three inches) applied in a flat layer over the root area can help keep the soil moist and cool and will also feed the soil as it breaks down slowly over time. Do not allow the mulch to touch the bark, keep it several inches away from the trunk.
It is certainly possible your tree was more advanced into its growth cycle when you purchased it than it would have been if it had been growing in your yard all along. Sometimes this tenderness early in the season can cause problems later. If the foliage was lightly frosted earlier in the season then that could be contributing to some of the tip or edge browning you are seeing now as a delayed result of frost damage. (This can happen on hostas also, where the damage is not apparent until the heat of summer hits.)
These trees are also sensitive to overfertilizing and other chemicals, so accidental exposure to drift, for example, can also cause foliage symptoms.
All in all the best thing to do for your new tree is to keep it watered. If you are still concerned about it, you might wish to consult with your retailer as well. Enjoy your tree, this is a lovely one!
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