hemlocks

Question

what would cause a hemlock small tree to drop all its needles in a few days

Answer 1

A diagnosis such as this requires a fair amount of investigation. Were the needles discolored before they dropped? How old is the tree? Was anything sprayed near the tree? Here is an article that will help you get started with a diagnosis: https://www.gardeningknowhow.com/ornamental/trees/tgen/why-conifers-drop-needles.htm