In a boundary dispute does occupancy over many years give ownership or does the boundary have to be redrawn and garden land given back?

You may have an adverse possession claim and should consult an attorney familiar with adverse possession claims in your state.

==Additional Answer==

Each state has its own laws on these matters. In California, you would probably have 'prescriptive right' which means you have had use of the property for a statutory number of years. Asking the Court to settle the matter, and having a boundary map prepared to recognize the changed property's configuration, should settle the matter.