Trees also need water in proper amount. During summer season, it is quite necessary to keep your plants moisturized. That can be done by watering them properly from time to time and make sure that they do not shrink due to heat and sunlight. Hydration in the roots of plants causes them damage. When the water is not reaching the roots, then it happens. The soil should not be very hard and water should go down to the roots.
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many ways to do this, I like the pvc one its very simple.