Just bought a weeping snow cherry and after about a week the leaves are starting to to yellow and drop. What can I do to save the tree?
Yellow Leaves on Weeping Snow Cherry
It sounds like the tree has been stressed by lack of water. If it's stil in the container, soak it overnight in a tub of water. If it's in the ground, slowly water with 10 gallons of water over a one hour time period. If it is water stress relates, the yellowing and dropping of leaves should lessen.
Since you didn't indicate your USDA hardiness zone, the leaf drop could be nature doing her thing. All cherries in our area (6b) are completely leafless.