Weeping willows typically grow near water sources, such as rivers and streams, and while they do grow well in wet soil conditions, they also grow well in slightly dry soil conditions. There is a balance, though, that is often hard to achieve since a weeping willow can wilt and yellow because of both over-watering and under-watering. Fortunately, in most environments and soil conditions, weeping willows rarely need supplemental waterings. However, in that first season while a new weeping willow is becoming established and used to its new environment, supplemental waterings will be necessary.
Wet the tree's roots if they look dry when you first receive your weeping willow. If your roots are wrapped in burlap or in a container, keep them moist. Plant your weeping willow as soon as possible, and in the meantime, store it in a cool and dark location (such as a garage) and keep the roots wet or the soil or burlap moist.
Water your weeping willow right after planting. Set a hose near the base of the tree and turn it on so the water slowly trickles out. Leave it there for three to four hours.
Check the soil for moisture conditions for the first growing season, especially when you are not receiving at least an inch of rainfall a week. Use a soil moisture gauge or check it by carefully digging into the soil with a trowel. When the soil is still dry after 4 to 8 inches, it is time to water your weeping willow with the hose. Water it with a slow trickle of water for about three to four hours near the base of the tree.