It is not permitted [to grow] mustard or safflower close to a field of grain. However, it is permitted [to grow] mustard or safflower close to a field of greens. It is permitted to grow [a diverse kind] close to a barren spot, to plowed terrain, to a stone wall, to a road, to a wall ten handbreadths high, to a ditch which is ten [handbreadths] deep and four wide, to a tree which covers the ground, and to a rock ten high and four wide.