The increasing demand for meat and milk has stimulated interest in the development and recovery of pastures. Although humic acids (HAs) have been shown to have a biostimulating effect on plant growth, their use in pastures remains relatively unknown. This study aimed to evaluate the growth of 'Brachiaria decumbens' at different HAs concentrations and application times. This study was conducted in a greenhouse with pots containing 1.5 L of soil collected in a degraded pasture. A trial was carried out in a randomized block design in which five HAs concentrations (0, 7.5, 15, 30 and 60 mg L-1 C) and four application times were used as follows: leaf spray 15 days after emergence (LS 15 DAE); LS 45 DAE; LS 60 DAE; and successive leaf sprays (15, 45 and 60 DAE). Stem height, diameter, forage production and root development were evaluated. Height and stem diameter measurements were performed weekly. At 45 and 90 DAE, a cut was made at a height of 10 cm to simulate grazing and to measure forage production. At 90 DAE, the root mass was assessed. The HAs used at the concentration of 60 mg L-1 C applied at 15 DAE promoted increases of 44% in plant height and 196% in forage mass. After the cut, the optimum concentration was approximately 40 mg L-1 C. Although the use of HAs promoted root development, successive applications had deleterious effects on the plant. HAs could improve pasture biomass production at a low cost if applied at the ideal concentration.