Warming-induced glacier retreat exposes bare rocks and glacial sediments, facilitating the establishment of soils. The dynamic interplay between climate, vegetation cover, and soil formation is poorly understood as time-series data are lacking. Here, we present postglacial soil formation during the past 23,000 years inferred from ancient DNA shotgun analyses of Lake Lama sediments targeting plants, soil-associated fungi, and bacteria showing postmortem damage signatures that verify their ancient origin. In the Late Glacial, we reveal basaltic weathering with high abundances of lichens, carbon, and arsenic cyclers, shifting to mycorrhizae domination and N cycling in the Holocene. We reconstruct podzolization starting with spruce forest migration in the Holocene, resulting in soil acidification and increased iron cycling. Our reconstruction of soil formation also contributes basic knowledge for the design of carbon-capture strategies using basalt weathering.