In order to fully exploit the enormous potential of functional monolithic nanowire/graphene hybrid structures in high-performance flexible devices, a better understanding of the influence of the graphitic substrate (GS) on NWs growth is crucial. InAs nanowires (NWs) were simultaneously grown on Si and GS with identical growth temperature, In-flux and V/III flux ratio via an In-catalysed growth technique. It is demonstrated that the GS is a more favourable platform for the growth of dense InAs NWs under highly In-rich conditions (low V/III flux ratio), whereas silicon is a more suitable substrate under a highly As-rich condition (high V/III flux ratio). It is shown that the GS enables NWs growth at high In-flux which has enormous potential for the fabrication of cost-effective nanodevices. Transmission electron microscopy analysis of the NW/GS interface confirms the NWs are well aligned on the graphitic substrate. This study opens new possibilities for the choice of suitable substrate for the optimal growth of NWs under various conditions.