Sheviis 1:5

Three trees belonging to three different owners can combine to form an orchard and one may plow an entire plot of 2,500 square cubits for them. Rabban Gamliel says that the space in-between the trees must be sufficient for oxen to pass through wearing their utensils, i.e. four cubits (about six feet).

Sheviis 1:6

If ten saplings are planted throughout a beis seah (the aforementioned 2,500-square-cubit plot of land), the entire beis seah may be plowed because of them until Rosh Hashana of the seventh year. If the saplings are not scattered throughout the plot, but they are planted in a row and/or surrounded by a fence, then one may only plow what is necessary.