Dihydro-tetraaza-acenes are promising candidates for future applications in organic electronics, since these molecules form crystals through an interplay between H-bonding, dipolar, and van der Waals interactions. As a result, densely packed π−π structures – favorable for charge transport – are obtained, with exceptional stability under ambient conditions. This study investigates growth morphologies of dihydro-tetraaza-pentacene and dihydro-tetraaza-heptacene on vicinal c-plane sapphire. Submonolayers and thin films are grown using hot wall epitaxy, and the structures are investigated ex-situ by atomic force microscopy. Molecular arrangement, nucleation densities, sizes, shapes, and stability of the crystallites are analyzed as a function of the substrate temperature. The two molecular species were found to assume a different orientation of the molecules with respect to the substrate. An activation energy of (1.23 ± 0.12) eV was found for the nucleation of dihydro-tetraaza-heptacene islands (composed of upright standing molecules), while (1.16 ± 0.25) eV was obtained for dihydro-tetraaza-pentacene needles (composed of lying molecules). The observed disparity in the temperature dependent nucleation densities of the two molecular species is attributed to the different thermalization pathways of the impinging molecules.