Reference for Kilayim 3:2
כָּל מִין זְרָעִים אֵין זוֹרְעִים בַּעֲרוּגָה, וְכָל מִין יְרָקוֹת זוֹרְעִין בַּעֲרוּגָה. חַרְדָּל וַאֲפוּנִים הַשּׁוּפִין, מִין זְרָעִים. אֲפוּנִים הַגַּמְלָנִים, מִין יָרָק. גְּבוּל שֶׁהָיָה גָבוֹהַּ טֶפַח וְנִתְמַעֵט, כָּשֵׁר, שֶׁהָיָה כָשֵׁר מִתְּחִלָּתוֹ. הַתֶּלֶם וְאַמַּת הַמַּיִם שֶׁהֵם עֲמֻקִּים טֶפַח, זוֹרְעִים לְתוֹכָן שְׁלֹשָׁה זֵרְעוֹנִין, אֶחָד מִכָּאן, וְאֶחָד מִכָּאן, וְאֶחָד בָּאֶמְצַע:
It is forbidded to sow [different] species [of seeds that are normally grown in large fields] in one bed, but [diffrent] species of herbs may be sown in one bed. Mustard and small peas are [considered] seeds, [while] large peas are [considered] herbs. [If] a border [around a bed] that had been one handbreadth high was lowered, it remains valid, because it was originally valid. A furrow or a [dried up] water channel that are one handbreadth deep, one may sow three [different] species of seeds, one [species] on one side, and one [species] on the other side and one in the middle.