Storing more carbon in soils, particularly at depth, could be an effective and readily available means to mitigate climate change. Current estimates of soil organic carbon (SOC) are based on sampling the first 30 cm of soil. Deep soils abound worldwide, particularly in the tropics, and many plants are known to grow deep root systems. In addition, root-derived carbon is more easily retained in soil than other forms of plant-derived carbon. Here, we report empirical evidence gained in southeast Asia that indicates that teak (Tectona grandis L. f.) and rubber tree (Hevea brasiliensis Muell.Arg) grow substantial amounts of fine roots at soil depths of several metres, irrespective of climate and soil type. We conclude that more precise and more depth-wise comprehensive measurements of plant roots are need to improve the way we manage natural and cultivated ecosystems with regards to climate change mitigation.