Answer: It sounds as though it is going through either heat or water stress. Sometimes excessive heat will cause a young maple to drop its leaves early. As it matures it should be able to hold the foliage until autumn. Water stress can also cause leaf drop. Your maple should be watered deeply once each week. I think the easiest way to do this is to make a water basin or watering well beneath each tree by mounding up soil all around (in a circle, about 12" from the trunk). Fill the basin with water, allow to drain, then fill a second time. Watering in this way will concentrate the moisture directly over the root mass and allow it to trickle down, wetting the entire root mass. Once each week should be all your tree needs.
Best wishes with your maple!
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