The cultivation of energy crops on degraded soils contributes to reduce the risks associated with land use change, and the biomass may represent an additional revenue as a feedstock for bioenergy. Switchgrass and giant reed were tested under 300 and 600 mg Cr kg⁻¹, 110 and 220 mg Ni kg⁻¹, and 4 and 8 mg Cd kg⁻¹ contaminated soils, in a two year pot experiment. Switchgrass yields (average aerial 330 g.m⁻² and below ground 430 g.m⁻²), after the second year harvest, were not affected by Cd contamination and 110 mg Ni kg⁻¹, but 220 mg Ni kg⁻¹ significantly affected the yields (55–60% reduction). A total plant loss was observed in Cr-contaminated pots. Giant reed aboveground yields (control: 410 g.m⁻²), in the second year harvest, were significantly affected by all metals and levels of contamination (30–70% reduction), except in 110 mg Ni kg⁻¹ pots. The belowground biomass yields (average 1600 g.m⁻²) were not affected by the tested metals. Contamination did not affect the high heating value (HHV) of switchgrass (average 18.4 MJ.kg⁻¹) and giant reed aerial fractions (average 18.9 MJ.kg⁻¹, stems, and 18.1 MJ.kg⁻¹, leaves), harvested in the second year, indicating that the biomass can be exploited for bioenergy.