Answer:
What Banquo means when he says, "There if I grow, / The harvest is your own” is this:
He owes any success he might have to Duncan.
Step-by-step explanation:
In this statement, we can see that Banquo was referring to the right of the claim that Duncan had to any success he might have. It is quite clear from this text that he really appreciates the help that Duncan has rendered to him, so any big benefits that he had could be attributed to his friend Duncan.