Water is often the key factor in the success of a new tree. If you planted a new tree this year, it needs water.
Make sure to keep your tree's soil moist, but not waterlogged.
Water trees at least once a week, barring rain, and more frequently during hot, windy weather. An irrigation bag, available at most hardware stores, can help to provide consistent water to your new tree.
When the soil is dry below the surface of the mulch, it is time to water. Continue until mid-fall, tapering off as lower temperatures require less-frequent watering.