Answer: Yellow leaves can be caused by many things including lack of nitrogen, insufficient light, water-logged soil (plant roots need oxygen to thrive), dry soil, or iron deficiency. Also, transplant shock can contribute to yellowing and is quite common. If new growth shows up as green, that might be the problem.
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. Use a soil probe (any long, pointed piece of metal or wood 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. Use the information above to determine how moist the soil is before automatically applying more water. It's essential that you allow your drip system, hose or whatever to run long enough for water to penetrate the appropriate depth. Depending on the size emitters, soil type, etc. this might take several or many hours. It is best to water slowly, deeply and as infrequently as possible. I hope this info is helpful.
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