Micro- and nano-structures of ZnO have been grown on substrates from flowing carrier gases in a tube furnace. We have investigated how variations in the carrier gas composition, gas flow rate and the position of the substrate control the formation and the morphology of the nanostructures. The source material was pure zinc powder evaporated in the temperature range 500ºC to 650ºC in flowing Ar plus oxygen at atmospheric pressure. It was found that precise control of the gas composition, gas flow rate, and growth time was necessary for reliable deposition. It was also found that zinc powder must be washed to remove the surface oxide. Scanning electron microscopy (SEM) images of samples grown from a Zn powder source show forested needles approximately 100 nm in diameter by 1 micron long, and faceted rods from 500nm to 700nm thick. Photoluminescence measurements at 4 K show a dominant line at ~3.36eV with additional features at 3.32 and 3.37eV. The line widths are ~ 3.5meV, indicating good quality material. The usual green-band emission is also observed.