Halakhah zu Sheviit 4:13

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).