A method for mounting rotor blades of a wind turbine, wherein the wind turbine has a rotor hub with three rotor blade ports, on which a respective rotor blade is to be mounted, with the following steps: turning the rotor hub until the first rotor blade port is in a 90° or in a 270° position, fastening a first end of a first section of a mounting arm to the first rotor blade port, wherein the mounting arm has the first section and a second section, which are coupled with each other via a hinge, so that the angle between the first and second sections (210, 220) can be varied, turning the rotor hub with the help of the mounting arm, until the second rotor blade port is in a 270° or in a 90° position, wherein the angle between the first and second sections (210, 220) of the mounting arm is varied while turning the rotor hub, horizontally lifting a first rotor blade, in particular by means of a rotor blade traverse and a crane rope, so that the first rotor blade is horizontally mounted to the second rotor blade port of the rotor hub, turning the rotor hub with the help of the mounting arm, until the third rotor blade port is in a 270° or in a 90° position, mounting the second rotor blade to the third rotor blade port, in particular with the help of a rotor blade traverse and the crane rope, turning the rotor hub with the help of the mounting arm, until the first rotor blade port is in the 90° or in the 270° position, demounting the mounting arm from the first rotor blade port, mounting a third rotor blade to the first rotor blade port, in particular with the help of the rotor blade traverse and the crane rope, wherein the angle between the first and second sections (210, 220) of the mounting arm is varied by the swivel hinge. turning the rotor hub until the first rotor blade port is in a 90° or in a 270° position, fastening a first end of a first section of a mounting arm to the first rotor blade port, wherein the mounting arm has the first section and a second section, which are coupled with each other via a hinge, so that the angle between the first and second sections (210, 220) can be varied, turning the rotor hub with the help of the mounting arm, until the second rotor blade port is in a 270° or in a 90° position, wherein the angle between the first and second sections (210, 220) of the mounting arm is varied while turning the rotor hub, horizontally lifting a first rotor blade, in particular by means of a rotor blade traverse and a crane rope, so that the first rotor blade is horizontally mounted to the second rotor blade port of the rotor hub, turning the rotor hub with the help of the mounting arm, until the third rotor blade port is in a 270° or in a 90° position, mounting the second rotor blade to the third rotor blade port, in particular with the help of a rotor blade traverse and the crane rope, turning the rotor hub with the help of the mounting arm, until the first rotor blade port is in the 90° or in the 270° position, demounting the mounting arm from the first rotor blade port, mounting a third rotor blade to the first rotor blade port, in particular with the help of the rotor blade traverse and the crane rope, wherein the angle between the first and second sections (210, 220) of the mounting arm is varied by the swivel hinge.