ZnO is a unique material that exhibits semiconducting and piezoelectric dual properties. Moreover the possibility of growing ZnO with a nanowire structure opens ways for promising applications in different fields such as solar cells, biosensors or UV detectors. This work reports the relationship between the properties of the substrate and the growth of high aspect ratio ZnO nanowires by pulsed injection Metal Organic Chemical Vapor Deposition (MOCVD). Indeed we demonstrate that the morphology of the substrate surface is one of the fundamental parameter for the nanowires growth without any catalyst. We have investigated various substrates (glass, silicon, SnO2, SiC,...) and have shown that for identical experimental conditions the material deposited can be either textured thin film, randomly orientated nanowires or vertically aligned nanowires.