We report the size-controlled growth of Ge nanowires from Au-Ag-Ge ternary alloy catalysts. Significantly, Au-Ag-Ge layered thin films enabled, for the first time, the synthesis of high aspect ratio Ge nanowires by simultaneously manipulating both the solute concentration (C) and equilibrium concentration (Ceq.) of Ge in the catalysts, thereby increasing the Ge supersaturation during vapour-liquid-solid (VLS) growth. Simultaneous manipulation of C and Ceq. to enhance nanowire growth rates was also achieved using colloidal Au0.75-Ag0.25 nanoparticles deposited on a Ge film. These nanoparticles produced Ge nanowires with more uniform diameter distributions than those obtained from the thin films. The manifestation of the Gibbs-Thomson effect, resulting in a diameter dependent growth rate, was observed for all nanowires grown from Au0.75-Ag0.25 nanoparticles. In situ TEM heating experiments performed on the as-grown Ge nanowires enabled direct determination of the Ge equilibrium concentrations in the Au-Ag-Ge ternary alloys.