Predictions of the global carbon budget and climate change depend in part on the factors that control soil organic matter behaviour and associated carbon storage. In cooler regions it is expected that carbon input to soils will increase under a warming climate that enhances vegetation growth and litterfall fluxes. There is also the potential for warming-induced carbon losses through soil respiration from these systems, making future behaviour uncertain. Soil organic carbon storage is generally considered to be controlled by soil texture and climate. We examined these patterns in detail using a comprehensive soil dataset for boreal and taiga regions of northern Saskatchewan, spanning a mean annual temperature gradient of ~7°C, which allowed us to investigate multiple controls on soil organic carbon. Despite the observed climate gradient, we found only a weak relationship between soil organic carbon and temperature, precipitation, and net primary productivity. Soil properties, including clay content and other particle size metrics were stronger predictors of soil organic carbon, however the strongest relationships were found for soil geochemistry. Soils with high silica and low aluminium and iron contents were associated with low carbon storage. Extending this relationship to other regions, including temperate forests and shrub and grassland sites in the Southern Hemisphere, we found that these strong correlations persisted. This analysis demonstrates the importance of soil geochemical properties, as well as texture, in protecting soil organic carbon, highlighting the importance of incorporating them in Earth System Models to better capture the behaviour of soil organic carbon stocks.