The aim of the four-year field experiment was to determine the effect of the foliar application of auxin, a synthetic growth hormone, used on its own and in combination with various iron concentrations on the yield and forage quality of Medicago x varia T. Martyn, the Kometa cultivar. The research was conducted in three replications at the experimental facility of Siedlce University (52°10′03"N; 22°17′24"E, Poland) between 2014 and 2017. The treatment combinations were as follows: K – control (distilled water); A – indole-3-butyric acid (IBA - synthetic auxin); A+F1 – auxin (indole-3 butyric acid) with iron (II) sulphate (IV) heptahydrate at 3% concentration; A+F2 – auxin (indole-3 butyric acid (IBA)) with iron (II) sulphate heptahydrate at 5% concentration; A+F3 – auxin (indole-3 butyric acid (IBA) with iron (II) sulphate heptahydrate at 7% concentration. Between 2014 and 2017 hybrid alfalfa was harvested at the beginning of the bud stage, three times a growing season. Each growth cycle, plants were sprayed once at the 9-leaf stage. During a harvest 0.5 kg of fresh matter was collected from each plot to determine the content of aboveground dry matter and to perform chemical analyses. The highest yield, 44% higher than for control plants, was noted on the plot treated with auxin applied together with iron sulphate at 5% concentration, and the lowest on the control plot. Foliar application of auxin with iron improved the quality of alfalfa forage, affecting the content of total and digestible protein and crude fibre and dry matter digestibility.