Large-scale growth capability is a general requirement for any reliable and cost-effective device application. Catalyst-free vapor-phase growth techniques generally let obtain high purity materials, but their application in large-scale growths of zinc oxide (ZnO) nanostructures is not trivial, because the lack of catalysts makes the control of these process rather difficult. Three different optimizations of the basic vapor phase growth have been studied and performed to obtain selected and reproducible growths of three different ZnO nanostructures with improved yield, i.e. nanotetrapods, nanowires and nanorods. No precursor or catalyst has been used in order to reduce contamination sources as more as possible.