Willow trees can be started by unconventional techniques. In fact, a
willow once was propagated by tossing a willow basket into a pit in the
yard of a house in Philadelphia. Eventually someone noticed that the
basket was growing into a tree.
You can root leafless, several foot long branches of first-year wood in
moist soil. And 9- to 12-inch hardwood cuttings, taken in the spring or
fall, will root if left in water. Even leafy summer cuttings will root.
The trees, however, are difficult to transplant. Prune them back
considerably at planting time, and brace yourself; the tree will recover
Willows are associated with soggy soil and indeed thrive in it. However,
they grow in almost any soil that is not extremely dry. Once
established, they grow fast and must be pruned to keep their good looks.
The shrubby species can be seriously chopped back; they may look
pathetic for several months but will burst forth into even bushier
Rodale's Illustrated Encyclopedia of Herbs
Rodale Press, Emmaus, Pennsylvania