Generally, I try to incorporate three or four inches of appropriate amendments into any new beds I dig. Fresh manure burns plant roots. And if you're adding peat moss, moisten it first. And incorporate all amendments well before planting. Willows like moist soil, and most do well in partial shade.
Weeping willows grow into massive trees with wide-ranging root systems.
If you have a large property near a natural pond or stream, go for it. A smaller willow is the Arctic willow, which does well in shady spots. There are several other species, too, so I'd suggest visiting a local nursery to see what's available. Thanks for your question. Choose varieties that are resistant to this, if you can.