Question
how fast do the grow..and how to prune..and fertilize

Answer
Weeping willows grow fairly fast, but are not large trees when fully grown.  They like water and require little care on your part.  If in a landscape setting you can prune but only is the limbs are hanging down and in the way of other plants.  Thats the beauty of the weeping willow--- the low lying branches.  Fertilize with a slow release tree fertilizer and keep watered during dry periods.  It should take care of itself otherwise.  Good Luck.