This objective of this study was to determine if mineralization of C, N, and P was pH stressed and/or nutrient limited in a bog and fen in northeastern Minnesota. Although soil activity in northern peatlands can be limited by low pH, low temperatures, high C:N and C:P ratios of soil organic matter, and/or anaerobic conditions, different classes of peatlands (bog and fen) vary in the type and degree of stress affecting soil processes. We employed in situ studies, laboratory incubations, and a fertilization and liming experiment to understand peatland mineralization dynamics further. Nitrogen mineralization in the field was higher in the fen than in the bog, but net P mineralization was close to zero in both sites. Soil cores were removed from plots that had been treated for 2 years with NH4+, PO4−2, and/or CaCO3, followed by a 30-week lab incubation. Nutrient additions in the bog increased the labile N pool (N0), and cumulative N and P mineralization over 30 weeks, but lime addition had no effect. Nutrient additions to the fen did not significantly alter nutrient pool sizes (N0, P0), cumulative mineralization totals, or mineralization rates. However, lime additions decreased potentially mineralizable N and cumulative N mineralization in the fen aerobic incubations, but increased cumulative P mineralization in the anaerobic incubations. Although both are peatlands, bog and fen nutrient cycles are controlled by different factors that may explain the differences in mineralization, total soil N and P, and respective labile pools. This information may be especially useful in anticipating changes brought about by anthropogenic nutrient/cation inputs and hydrologic alterations.