Implied question: [How do we learn five species from] Zeru'eha? The least Zeru'eha could mean is two (we cannot learn more than this)!

Answer #1 (R. Shmuel bar Sisarta): From two you learn four. Just like two, [if one wants to maximize the sown area,] at the beginning (e.g. on the north side) you put (plant all) six [Tefachim] and keep narrowing [the sown part until the point in the middle, and similarly from the south side], so you can plant four - you put (plant) three [Tefachim on the west half of the north side] and keep narrowing [until the point in the middle of the west half of the patch, and similarly from the west half of the south side. You similarly put two species in the east half of the patch. It is impossible that there will not be a point free to plant [the fifth species in] the middle [of the patch].

(R. Yonah): [When two species are planted on opposite sides of a line,] Avodah encounters Avodah (and they must be separated), but a species [that narrows to a point] does not encounter another [such] species to constrict it (obligate separation. We explained this like R. SHLOMO SIRILIYO, Kil'ayim 3:1.)

Answer #2 (R. Yehoshua ben Levi): [The verse could have said] Zera [to teach one, or] Zar'eha (to teach another two. Rather, it said) Zeru'eha [to teach another two, i.e. five in all]. According to R. Yehudah, that R. Yehudah says [that one may plant] six [species, for the verse could have said] Zera [to teach one], Zar'ah [to teach another] Zar'eha [to teach two more, and rather, it said] Zeru'eha.

Answer #3 (R. Chagai): [The word is written without a Vov, as if it said] Zar'eha (therefore Chachamim do not learn like R. Yehudah. R. Yehudah says six, for he expounds based on how we pronounce it.) Anywhere that I see [the word written with a Vov], I will erase it!

They asked Rav Huna the scribe of the Beis Midrash. He said that Zeru'eha is written full.

(R. Yochanan citing R. Yanai): All of [the species] are seeded outside of the six [Tefachim].

Question: If all of them are outside of the six, he should teach nine (one in the middle, one just outside each corner, and one just outside the middle of each side)!

Answer (R. Tanchum Botzrei): Our Mishnah discusses a patch amidst other patches. (If he would sow nine in this patch, he could sow the sides of the surrounding patches.)