Salt marshes created on dredge spoil were compared to natural marshes to evaluate the capacity of created marshes to perform carbon cycle functions. Several carbon cycle attributes were measured in eight created Spartina alterniflora Loisel salt marshes that ranged from one to 28 years, each paired with a nearby mature natural reference marsh. The attributes measured included gross primary production, respiration, net ecosystem exchange, potential microbial respiration (CH₄ and CO₂), and aboveground biomass. In situ exchange rates of CO₂ and plant biomass in created marshes met or exceeded those of reference marshes in three to four years. There was some evidence that ecosystem gas exchange in created marshes developed slightly faster than aboveground biomass production. Soil carbon mineralization per gram carbon was generally higher in the created marshes than reference marshes, suggesting higher carbon quality and/or nutrient availability in the created marshes. However, carbon mineralization rates per gram soil were relatively low in the created marshes due to lower soil organic matter content. With proper construction, we suggest most major carbon fluxes can be established in created salt marshes in less than five years.