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Hierarchically porous carbon (HPC) derived from fallen flowers was prepared by a green method of combining solvent-free ball milling with the safe activating agent potassium bicarbonate. By regulating the mass ratio of KHCO 3 to biochar, the as-prepared HPC materials possess high specific surface areas of up to 2147.9 m 2  g -1 and abundant hierarchical pores comprised of micro-, meso-, and macropores. The specific capacitances of the HPC materials are able to reach 302.7 F g -1 at a current density of 0.5 A g -1 in 6 m KOH, and the symmetric supercapacitor composed of two identical HPC electrodes shows good stability because 100 % of the specific capacitance is retained after 5000 charge/discharge cycles and 90.5 % of the specific capacitance remains after 12 000 cycles. Nitrogen self-doped HPC materials also show higher electrocatalytic activity and stronger methanol tolerance for the oxygen reduction reaction than that of the commercial Pt/C catalyst. This preparation method can be extended to the green conversion of other varieties of biomass waste into useful carbon materials., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)