Tosefta do Challa 1:15

We do not take terumah from produce [that is harvested] before it is one-third ripe (cf. Hallah 1:3). How do you know if it is one-third ripe or if not? If it is planted and something has sprouted, it is known that it one-third ripe. If it is planted and something has not sprouted, it is known that it is not one-third ripe.