Methods for joining surface features to wind turbine rotor blades are provided. A method includes providing the surface feature after forming of the rotor blade. The surface feature includes a thermoplastic resin. The formed rotor blade includes a plurality of blade components joined together to form an exterior surface defining a pressure side, a suction side, a leading edge, and a trailing edge each extending between a tip and a root. The formed rotor blade further includes a thermoplastic resin. The method further includes positioning the surface feature adjacent the exterior surface, and welding the thermoplastic resin of the surface feature and the thermoplastic resin of the formed rotor blade together.