LAUSR

Abstract Humic acid (HA) as a major portion of humic substances and organic matter play an important role in soil fertility and environmental sustainability. Previous studies reported an enormous range of responses after HA application on plants. To investigate the influence of HA on pelargonium plants cv. ‘Hortorum’ this study was conducted as a randomized complete block design under greenhouse condition. Treatments included HA at 0, 250 and 500 mg L−1 concentrations that were added into the soil via irrigation. Application of HA at both 250 and 500 mg/L promoted plant growth characteristics; however, application of 250 mg L−1 of HA showed better improvement in terms of numbers of leaves, numbers of flowering shoots, and numbers of flowers per plant. Moreover, the length and diameter of the flowering shoot, inflorescence diameter, fresh weight of the aerial parts per plant, and leaf nitrogen (N) were improved only by 250 mg L−1 of HA application.