(R. Yehoshua ben Levi): One can expound the word Zeru'eha based on each extra letter that the Torah added - Instead of 'Zar'ah', it added a letter 'Yud' that becomes 'Zar'eha' and it also added a letter 'Vav', to become Zeru'eha (so it's as if it wrote 'Zar'ah Zar'eha Zeru'eha', which is singular plus plural plus plural, totalling five).

This is similar to the way R. Yehuda learns - (but he starts one step earlier, saying that the Torah could have written 'Zerah', but instead it wrote 'Zar'ah' (with an extra letter 'Hei') etc. (so it's as if it wrote 'Zerah Zar'ah Zar'eha Zeru'eha', which is singular plus singular plus plural plus plural, totalling six).

(R. Chagai): There are five letters in the word Zar'eha - wherever it's also written with a Vav, I erase it.

It was asked to Rav Huna, the arranger of pesukim (who was an expert in the correct spelling of words in the Torah), and he said that the correct spelling of the word is Zeru'eha is to be written in full (with the letter Vav).

(R. Yochanan citing R. Yannai): When the Mishnah allowed 5 species, it's when they are all planted within the 6 Tefach bed.

(Kahana citing R. Shimon ben Lakish): Even when one wishes to plant near the bed, he may only plant 5.

Question: If so, the Mishnah should teach that 9 rather than 5 species may be planted?

(R. Tanchum of Butzra): The Mishnah permitted (planting on the border) even when the bed is planted adjacent to other beds.