The morphologies and unique properties of zinc oxide nanoflowers make the nanoflowers promising candidates for use in wide range of future technological device applications. This paper describes the use of a versatile single-step synthetic route for producing ZnO nanoflowers under hydrothermal conditions at various reaction times. High-quality ZnO crystal was obtained after only 4 h by using this synthetic route. The morphology evolution and the length of rods that compose the flowers were monitored using SEM and ImageJ software. From the SEM images, it was possible to identify the formation of pure ZnO nanoflowers after 15 min under hydrothermal conditions. The length of the nanoflowers and the presence of defects in their morphology directly affected their optical properties, as examined using UV–visible and photoluminescence spectrophotometry. For samples kept at 5 and 10 min under similar conditions the time was not enough to form nanoflowers of pure ZnO materials. Actually, the samples are composed by two phases with zinc hydroxide being majority (>95%) and morphology like-rods.