This is the commercial method of propagating hardwood from cuttings. In the coldest part of winter, take cuttings at least the thickness of a thumb. Cut to about 5" lengths. Place upside down in a pail filled with sand. Fill with water to the top of the sand. Keep in cool place, but frost-free. In spring, you will find little knobs on the sticks where roots will set. That's the right time to set each one right side up in a pot of soil. Water.

This works for willow, poplar, dogwood, and other hardwoods which produce their own rooting hormones. You can test for suitability of a species by placing a twig in water. If roots form by themselves, the species can be used.

If you have soaking wet ground in the spring, you can stick willow branches directly into the wet ground as soon as the frost is gone out of the soil. They root more easily than any other species. One warning: Do not plant willow or poplar within 100' of a building. The roots go wandering, looking for water. They end up plugging sewer lines. All the above hardwoods are water-loving plants and should not be planted unless the conditions are right. You have to have really wet springs to satisfy their thirst.