Nanographenes and polycyclic aromatic hydrocarbons (PAHs) are among the most important classes of compounds, with potential applications in nearly all areas of science and technology. While the theoretically possible number of nanographene structures is extraordinary, most of these molecules remain synthetically out of reach due to a lack of programmable and diversity-oriented synthetic methods, and their potentially huge structure-property diversity has not been fully exploited. Herein we report a diversity-oriented, growth-from-template synthesis of nanographenes enabled by iterative annulative π-extension (APEX) reactions from small PAH starting materials. The developed dearomative annulative π-extension (DAPEX) reaction enables π-elongation at the less-reactive M-regions of PAHs, and is successfully combined with complementary APEX reactions that occur at K- and bay-regions to access a variety of previously untapped nanographenes.