We present a dephasing time analysis of the excitonic resonances in Ge/SiGe quantum wells for various lattice temperatures by coherent oscillation spectroscopy (COS). The results are compared to the linewidths of the excitonic resonances determined from linear absorption measurements. Additionally, COS is applied to different samples with varying linewidth, identifying one sample with a dominating homogeneously broadened 1s excitonic resonance down to 7 K.