The easiest way to propagate most Ficus trees is to use cuttings. Cuttings of any size Ficus generally will root. However, some people prefer to use an air-layering process as this can be a safer way to propagate a specific piece.
Ficus salicaria that should be shortened
A groove is created around the area in which roots are desired
A plastic bag with sphagnum moss is wrapped around the grooved area- water the moss to keep it moist
Once roots fill the bag the air-layer is cut off
The top of the tree with all the moss is placed into a pot and watered normally. The lower section of the tree will sprout out in 1-3 months.