I have not had any luck growing begonias in the ground.  Snails always devour nearly every portion of the plant.  I have the same problem with dahlias.  Snails consume the leaves so quickly as they grow above the ground that the tuber does not have a chance to develop a stem.  

A few months ago, I purchased the above-pictured full-grown begonia from a nursery and planted it in a hanging container.  I figured the snails were unlikely to get to it here.  So far, I have not noticed any holes in the leaves.  It continues to bloom and look great.