A general rule about which foods must be tithed: Any [plant] which is eaten by people, and is gathered, and grows from the ground, is liable for tithes. Another general rule was said: Any fruit which is edible at both the early and late stages of growth, even though [the farmer] delays picking it so that it will increase, it is liable for tithing whether small or large. But any fruit which is not edible until it grows larger is not liable for tithing until it becomes edible.
If tithing is a divine mandate, then doing it properly is of paramount importance. This Mishnah is a window into the daily reality of the Israelite farmer evaluating his crops for both economic and spiritual purposes.