Sefer HaChinuch ספר החינוך

That we not harvest the aftergrowth on the seventh year: That we not harvest that which grows on its own from the land on the seventh year, nor the growth that occurs on this year from what was sown in the sixth year — and this is called aftergrowth — as it is stated (Leviticus 25:5), “The aftergrowth of your reaping you shall not harvest.” This means to say that we not harvest it in the manner that we harvest our crops in other years. (See Sefer HaMitzvot, Negative Commandments 222.) Nevertheless, eating was permitted to us, provided that it is eaten in a way [that shows that it is] ownerless — meaning without preparation, as we will explain in the commandment after this (Sefer HaChinukh 329). As the Torah’s only concern in these matters was that a person’s actions during this year should indicate that he has no specific property, but that everything is the property of the Master of All — and as we said above.

What is written about this matter (in Sefer HaChinukh 84) is from the roots of the commandment.

From the laws of the commandment is that which they, may their memory be blessed, said (Mishnah Sheviit 4:2) that even if a person transgressed and planted his field in the seventh [year] and [its produce] grew, the produce is permissible on a Torah level; so long as it is not harvested in the way of the harvesters on all other years — such that they harvest the whole field and bundle it into a threshing floor and thresh it with oxen. Rather from Torah writ, the law is to harvest a little at a time, to pound [it] and to eat. But the Sages decreed that [even] the aftergrowth be forbidden for eating, on account of the transgressors that would sow their garden in the Fall and say, “It is [only] aftergrowth.” And this decree is only with vegetables, grains and legumes, as it is the way of people to plant them. But fruits of the trees and grasses — which is not the way of people to sow — are permitted. (See Mishneh Torah, Laws of Sabbatical Year and the Jubilee 4.)

And this commandment is practiced from Torah writ by males and females in the Land of Israel at the time that Israel is there. And regarding the other places, it is all as I have written (Sefer HaChinukh 84). And one who transgresses this at the time of the [Temple] and harvested the produce that he sowed in the way of the harvesters — such that he harvested the whole field and bundled it into a threshing floor and threshed it with oxen in the way that people do on other years — is lashed. And one who gathers from the aftergrowth of produce that is sown — even though he does not harvest it all together — is struck with lashes of rebellion; since the Sages decreed about it, as we said.