Newly planted trees have to make a transition from the limited resources but constant care of the nursery, to the much larger resource base but much less frequent care they will get once established in the landscape. It takes them a bit of time to make this transition. Water very well at planting, and for the first month or so, water a few times per week, making sure the original root ball is getting moistened. Feel this soil prior to watering, however, to avoid adding water to an already wet soil – that could lead to root dieback and rotting. Over time, water less often but with more water at each irrigation event.