Shabbat 85B

גזירה שמא ימלא את הקרנות. ולא יהא אלא ראש תור ירק? מי לא תנן: היה ראש תור ירק נכנס לתוך שדה אחר ⁠— מותר, מפני שנראה סוף שדה! אין ראש תור בערוגה.

Rather, Rav’s reasoning must be: It is a decree lest one will fill the corners after having first planted the garden bed, and thereby violate the prohibition of diverse kinds. The Talmud asks: And why should that matter, the legal status of the garden bed should merely be like a triangular [rosh tor] plot of vegetables. Didn’t we learn in a Mishnah: If a triangular plot of vegetables was protruding into another field, it is permitted; there, it is not considered a prohibited mixture of diverse kinds, because the end of the field is distinguishable. Based on the shapes of the two fields where they intersect, the demarcation between them is clear. And the Talmud answers: There is no leniency with regard to a triangular plot in a garden bed. This allowance with regard to a triangular section of one field jutting into another field applies only to a large field where the triangular shape can clearly be attributed to a different field, but in a small garden bed where the seeds are adjacent to one another, it is impossible to distinguish between the seeds.

ושמואל אמר: ערוגה בין הערוגות שנינו. והא קא מיתערבי בהדדי! בנוטה שורה לכאן ושורה לכאן.

And Shmuel said: When we learned in the Mishnah that one may plant 5 kinds of seeds within a garden bed without violating the prohibition of diverse kinds, we learned this even with regard to a garden bed among garden beds, not only in a solitary bed. The Talmud asks: Don’t the seeds become intermingled with one another? The Talmud answers: It is referring to a case where one inclines one row to here, in one direction, and one row to here, in a different direction (Me’iri). In that way they do not appear intermingled.