Willow has an enormous growth power and will grow in almost any soil condition when established.
I had used some clippings from my willows for a Christmas decoration along with cuttings from a blue spruce and the beautiful seed heads from my irises. To prevent the spruce from drying out and drop it's needles, I stuck it all in wet oasis and kept it moist all the time.
The cuttings from my Dragon Willow (Salix sachaliensis 'Sekka') started to root and grow almost immediately. I kept removing the shoots until just after Christmas and then I just left it alone.
Yesterday, when I wanted to "dismantle" the decoration to throw it out, it looked like this. The willows had rooted in the oasis, had numerous shoots and even a couple of catkins.
Willows contain a natural chemical called indolebutyric acid IBA which is a natural plant growth hormone and you can actually make your own "rooting hormone liquid" from willow twigs.
Because of this, the most common method for propagating willow is by cuttings.
You just cut a piece, the size of a pencil, (preferably from a one year old shoot during the dormant time of the year) and stick it in the soil. Keep it moist and it will grow.