Answer: Without more detail on your plant's age, care and growing conditions, it's difficult to say exactly what the issue is, but in the arid west and southwest, drying leaves are often a signal that the plant is not absorbing sufficient water. This can be because the rootball was wrapped too tight around itself when transplanted, and the roots aren't growing out into the surrounding soil. More likely, it is not receiving sufficient water. Use a soil probe (any long, pointed piece of metal to poke into the soil) to check how far water has penetrated. The probe moves easily through moist soil, but stops when it hits hard dry soil. There are numerous variables involved for watering schedules, such as type of soil, how fast or slow it drains, sun and wind exposure at your site, temperature, age and condition of the plants and much more. For mature trees, water should soak 3 feet deep; for newly planted trees, about 2 to 2.5, depending on the size/depth of the rootball when it was planted. Water should be applied at the edges of the tree's canopy and slightly beyond. This is where feeder roots are actively absorbing water. If you use a hose, let the water run long enough to reach the depth above. If you use drip, depending on the number and flow rate of emitters, you may need to let it run for several or even many hours to apply sufficient water. For example, an emitter that puts out one gallon per hour would only put a quart of water on the ground in 15 minutes. As trees grow, emitters need to be moved outwards to keep pace with the expanding canopy.
Also, dried leaves can be a sign of fertilizer or salt burn, which shows up as yellowing, then browning around leaf edges, and dried out leaves. Newly planted trees usually don't require fertilizer for one year. Always follow package instructions for amounts, and water well after applying.
Soil and water both contain salts, which can accumulate in the root zone over time. This salt buildup forms where the water stops penetrating. Short periods of watering cause salts to build up in the top layers of soil and damage or kill your plant. Deep watering?or leaching?prevents this by flushing the salts past the root zone. Always water slowly, deeply and as infrequently as possible. I hope this info helps.
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