Answer: The symptoms sound like heat stress and as your birch trees mature they should be able to tolerate the summer weather. My concern is with your watering practices. Clay soil tends to hold moisture for great lengths of time so daily watering is not a good idea, especially a "little" water. All you're doing is teasing the trees and encouraging the roots to remain close to the soil surface where the moisture is. Instead of daily watering, water deeply once or twice a week during the summer months. The easiest way to do this is to build a water well or water basin beneath each tree by mounding up a few inches of soil in a circle around the tree, about 12 inches away from the trunk. Fill the basin with water, allow to drain, then fill a second time. Watering in this way concentrates the moisture over the entire root mass and allows it to trickle down, wetting the entire root system. Do this once or twice a week and your birches should establish well and be able to tolerate hot summer weather. Good luck with your trees.
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