The application of mechanically crushed silicate minerals to agricultural soils has been proposed as a method for both improving crop yields and sequestering inorganic carbon through enhanced mineral weathering. In Greenland, large quantities of finely grained glacial rock flour (GRF) are naturally produced by glacial erosion of bedrock and deposited in easily accessible lacustrine and marine deposits, without the need for energy-intensive grinding. To determine if this material can improve crop yields, we applied 10 and 50 t GRF ha⁻¹ to a sandy, organic agricultural field in Denmark. Two field trials were carried out to test the first-year yield response to GRF in both maize and potatoes, residual effects on potato yields in the year after application, and second and third-year residual effects on spring wheat. Reference-K treatments were included for comparison to determine if the beneficial effects of GRF were primarily due to its K content (3.5% K₂O). This alternative source of silicate minerals improved crop yields in the year of application. Though there was no improvement in yield with the reference-K treatments, for each additional ton of GRF applied, maize dry yield increased by 59 kg ha⁻¹ and potato tuber yield by an additional 90 kg ha⁻¹. No residual effects on crop yields were observed in the following years, but we suspect that benefits might persist over multiple seasons at sites with lower initial fertility. The increase in yields achieved with GRF could offset some of the costs of applying silicate minerals as a CO₂ sequestration scheme.