Hilchos Shemittah v’Yoveil 4:1

Let’s discuss produce that grows from the ground during shemittah – both those that grew from seeds that fell to the ground before shemittah and those that grew from the roots of plants that were harvested before shemittah. Both of these types of produce are called “safiach,” meaning vegetation that grew on its own during shemittah. Such produce may be eaten under Biblical law, as per Leviticus 25:6: “(The produce of) the land’s rest will be yours to eat.” Even if a field was plowed during shemittah, produce that grew in it may be eaten. “Do not reap the safiach of your harvest” (Leviticus 25:5) means not to harvest it the same way that one does in every year. If one harvests in the regular manner, he is liable to the penalty of lashes. An example of the regular manner would be if someone harvests his whole field, makes a grain pile, and threshes it with cattle or harvests it in order to work the land, as has previously been discussed. Rather, one must harvest his field a little a time, beat the grain (rather than threshing it) and then eat it.

Hilchos Shemittah v’Yoveil 4:2

Under Rabbinic law, safiach may not be eaten. This rule was instituted in order to keep people from secretly planting grain, beans and vegetables in their fields so that when they grow they could eat them and claim that they were safiach. In order to prevent this, the Sages prohibited all safiach that grows during shemittah.