Harrow, HAR oh, is an implement that farmers use to break plowed earth into smaller pieces before they plant seeds. The clods of earth left by the plow are too large for the delicate shoots to break through and too rough for machines to travel over during cultivation and harvesting. The harrow is also used to kill weeds and cover newly sown seeds. There are three main types: (1) the disk harrow, (2) the spike-tooth harrow, and (3) the spring-tooth harrow.