quantity of fruit, or does it mean that one-third of the zakah is placed at the owner’s disposal, for him to distribute as he sees fit?

The correct view is that this is not a case of waiving zakah; rather, the owner is given discretion over it, since he may have relatives, friends, and the like to whom he gives from the zakah. What supports this as the stronger opinion is the general purport of the Prophet’s statement: “For that which is watered by the rain, one-tenth is due.” (1)