Northern peatlands store 455 Pg of carbon–a third of the entire global carbon store. Carbon accumulates because phenolic inhibitors slow the rate of decomposition to below that of photosynthetic production. The disproportionate importance of phenolics in peatlands is related to the unique properties of waterlogged peat soils suppressing the activity of phenol oxidase; one of the few enzymes capable of breaking these inhibitors down (a role often referred to as the “enzymic latch”). This permits accumulation of phenolic compounds that are potent inhibitors of hydrolase enzymes–major agents in the breakdown of organic matter. In our study we investigate the importance of the molecular weight of phenolics on levels of inhibition of microbial decomposition in peat. We found the higher the molecular weight, of a phenolic compound, the greater its inhibitory effect on the breakdown of organic matter.