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Nanostructuring a material permits control over its interaction with light. Advanced methods for controlling the visible-to-infrared absorption spectra of semiconductor materials would present opportunities for photodetectors with engineered spectral response. Here, we experimentally demonstrate the fabrication of arrays of vertical Ge nanowires with different diameters. Measured reflection spectra show dip features for which electromagnetic simulations predict enhanced absorption. These can be shifted to longer wavelengths by increasing the diameters of the nanowires. We show that the reflectance dips broaden if the nanowires exhibit tapering. We furthermore show that observed ripple features in the dips are associated with longitudinal modes of the nanowires.