Trees and shrubs need extra water during their first couple of years to help roots take hold. An efficient way to keep roots moist is to mound several inches of soil into a donut-shaped berm. Make the berm the width of the tree—including branches.
Use a hose or bucket to fill the donut dam to the top. Water will absorb slowly instead of running off.
Another option: Attach a $25 to $30 drip irrigator bag to the tree. It looks like a plastic flotation tube and releases water slowly over several hours.