Tosefta for Terumot 9:7

הַמְנַכֵּשׁ עִם הַנָּכְרִי בַּחֲסִיּוֹת, אַף עַל פִּי שֶׁפֵּרוֹתָיו טֶבֶל, אוֹכֵל מֵהֶם עֲרַאי. שְׁתִילֵי תְרוּמָה שֶׁנִטְמְאוּ, שְׁתָלָן, טָהֲרוּ מִלְּטַמֵּא, וַאֲסוּרִין מִלֶּאֱכֹל עַד שֶׁיָּגֹם אֶת הָאֹכֶל. רַבִּי יְהוּדָה אוֹמֵר עַד שֶׁיָגֹם וְיִשְׁנֶה:

One who weeds with a non-Jew in leek-plants, even though its fruits are non-tithed, he may eat from them in a casual fashion. Saplings of <i>Terumah</i> which have become impure, if planted [again], they become pure from their impurity. But they may not be eaten until the edible [parts] have been lopped off [and regrown]. Rabbi Yehudah says: until they have been lopped off and repeated [lopped off a second time].

Tosefta Terumot