Abstract <p>The responsiveness of flax to mineral fertilizers and foliar top dressing with an aqueous solution of the drug Controlfit-Si on sod-podzolic medium loamy soil was studied. It is shown that the reaction of flax to mineral fertilizers depended on the hydrothermal environmental conditions, doses, and the ratio of nutrients. Excessive humidity and arid conditions negatively affected the productivity of crops. Foliar top dressing of plants with Controlfit-Si levelled the negative impact of adverse weather conditions, increased the responsiveness of plants to mineral fertilizers, and contributed to a more complete use of nutrients from fertilizers. On average, over 3 years, top dressing with full mineral fertilizer increased the yield of flax straw by 25–30%, with the best effect observed against the background of N48P48K48 (4.03 t/ha). Top dressing did not have a positive effect on the yield of flax seeds. It took 13.8 kg N, 5.9 kg P₂O₅, and 10.7 kg K₂O to form 1 t of flax crop with the appropriate number of seeds, regardless of plant nutrition conditions.</p>