Answer: Newly planted trees need careful attention to watering for at least a full year after planting. The soil should be kept slightly damp any time it is not frozen. If it is too wet or too dry, there can be root damage leading to defoliation.
Your goal in watering is to keep the soil evenly moist like a wrung out sponge, not sopping wet and not dried out. To know if you need to water, dig into the soil with your finger. If it is still damp, do not water yet. When you do water, apply it to the soil surface and water thoroughly and slowly so it soaks down to the deeper roots. After watering, wait a few hours and then dig down to see how far the water soaked in; it can be surprising.
There is no set schedule for watering, it depends on your soil type and on the weather. Using an organic mulch several inches thick over the root area will help reduce watering needs as well as feed the soil gradually as it breaks down over time.
If you think you have been watering correctly, there may be a pest or disease problem. I would suggest you consult with your local county extension to try to get a specific diagnosis and based on knowing that, decide what to do. Good luck with your tree!
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