Abstract: A machine is provided for the root-pruning of plants growing in rows, such that the root system of the plants will be small in circumference but finely-branched. The machine has, for each plant row, a knife unit for forming a groove in the ground and root-pruning the plants. Each knife unit comprises a first and second knife, wherein the first knife is forward of the second knife and lies in a vertical plane parallel to the direction of travel of the machine. The second knife has a cutting blade comprising a substantially vertical blade portion and a substantially horizontal blade portion. The first and second knives are rigidly interconnected and arranged for reciprocatory movement in a direction parallel to the direction of travel of the machine. A compactor is disposed behind the second knife for reclosing the groove made in the ground by the knife unit.