Reference for Chullin 231:7

כלאי הכרם עיקרן נאסר והיתה להן שעת הכושר קודם השרשה

therefore informs us that the original roots of divers kinds sown In a vineyard are forbidden, so that there was a time when these kinds had a period of fitness, namely, before they took root.

Jastrow

Jastrow