We have received reports of trees being slow to leaf out. In most cases this is likely just a cool spring delaying leaf emergence and we need to give them a bit more time. However, the very warm, dry winter coupled with cold snaps may also have caused some winter damage as evidenced by delayed leaf emergence or scorched leaves. Check that twigs are still supple. If they are brittle, that part of the tree is dead. There isn’t much that can be done to speed up leaf emergence other than avoid any further stress.
Try to water plants once a week for young or recently transplanted trees if you do not receive rainfall. Established trees should be watered every three weeks. Trees should be watered to a depth of 12 to 18 inches if possible. Water from the trunk to the outer edge of the branches.
Though this will not reach all the roots of a tree, it will reach the majority of them. Trees
normally have at least 80 percent of their roots in the top foot of soil. Shrubs should be watered to a depth of 8 to 12 inches. Check the depth of watering by pushing a wooden dowel or metal rod into the soil. It will stop when it hits dry soil. (Ward Upham)