We have reported low temperature growth (300 degrees C) of ZnO nanorod flower structures by depositing zinc acetate vapor on Ge (100) substrate in the form of a jet using chemical vapor condensation technique. The flowers were comprised of hierarchical arrangement of highly crystalline ZnO nanorods oriented isotropically around a common nucleus. The temperature window for stability of these structures was found to be very narrow and the formation of the flowers was highly depended on the type of the substrates used. The flower morphology changed to a different hemispherical shape when the growth temperature was increased by only 50 degrees C while decreasing the growth temperature of the same degrees resulted in an amorphous deposition of ZnO. The temperature and substrate effect has been explained on the basis of adatom kinetics during growth. X-ray diffraction and TEM study revealed wurtzite ZnO nanorods with lattice constants a and c of 3.2 and 5.19 angstrom, respectively. The flower structures showed strong room temperature photoluminescence having pure excitonic transition at around 3.298 eV. (C) 2009 Elsevier B.V. All rights reserved.