Vertically-oriented zinc oxide (ZnO) nanowires were synthesized on glass and silicon substrates by Pulsed Laser Deposition and without the use of a catalyst. An intermediate c-axis oriented nanotextured ZnO seed layer in the form of nanowall network with honey comb structure allows the growth of high quality, self-forming, and vertically-oriented nanowires at relatively low temperature (<400 degrees C) and under argon atmosphere at high pressure (>5 Torr). Many parameters were shown to affect the growth of the ZnO nanowires such as gas pressure, substrate-target distance, and laser energy. Growth of a c-axis-crystalline array of nanowires growing vertically from the energetically favorable sites on the seed layer is observed. Nucleation occurs due to the matching lattice structure and the polar nature of the ZnO seed layer. Morphological, structural, and optical properties were investigated. X-ray diffraction (XRD) revealed highly c-axis aligned nanowires along the (002) crystal plane. Room temperature photoluminescence (PL) measurements showed a strong and narrow bandwidth of Ultraviolet (UV) emission, which shifts to lower wavelength with the increase of pressure.