Answer: I think your trees are getting too much water. They haven't been in the ground long enough for the roots to become established so you should expect to see some stress through the rest of the season. But, overwatering is complicating matters. If possible, turn off the sprinklers nearest the trees. Your new trees need one inch of water per week. Since you have sandy soil you may want to water deeply every 4-5 days during hot weather, changing to once each week in spring and fall. The best way to water is to build a watering basin or water well directly beneath each tree. Remove the rocks from around the trees and make a watering ring. A water ring, sometimes called a water well, is a mound of compacted soil that is built around the circumference of a planting hole once a plant has been installed. The water ring helps to direct water to the outer edges of a planting hole, encouraging new roots to grow outward, in search of moisture. The height of the mound of soil will vary from a couple of inches. Your can then replace the rocks. When you water, fill the basin, allow it to drain, then fill it a second time. This should provide all the moisture your trees will need and will help them establish their roots and regain their health.
Best wishes with your landscape!
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