3,053. When You Can Plant Five Species in One Row

Hilchos Kilayim 4:10

The previous halacha (about planting five species in the same row) applies to planting in a ruin so that there are no other crops outside this row. If this row is among other rows, then it is prohibited to plant five species. This is because if he plants the four sides of the row plus the four sides of the rows around it, it will appear that he has planted mixed species. If he bends the leaves of one row to one side and the leaves of the other row to the other side to make them visibly distinct, then it is permitted. Similarly, if he digs a ditch between the rows, it is permitted.

Hilchos Kilayim 4:11

It is prohibited to plant outside the aforementioned row without a ditch or leaning the leaves; this is true even opposite the corners of the row, which are not planted. This is a rabbinic enactment made out of concern that one might end up planting four species in the four corners of the row and other species outside the row opposite those corners, thereby making it look like mixed species.