Effect of humic acid application and CPPU spraying on growth and flowering of Marigold

Abstract

This study investigated the effects of humic acid (HA) and forchlorfenuron (CPPU) on the growth, flowering, and chemical characteristics of marigold (Tagetes ereta L.) during the 2025 growing season under protected cultivation. The experiment was conducted using a factorial arrangement with two factors: three concentrations of HA (0, 2, and 4 mL L-1) and four concentrations of CPPU (0, 4, 8, and 12 mg L-1). Growth parameters, flowering traits, and biochemical contents were measured. Application of HA significantly improved all evaluated traits, with the highest values obtained at 4 mL L-1, resulting in plant height (37.67 cm), number of branches (6.84 plant-1), number of flowers (7.88 plant-1), flower diameter (6.68 cm), fresh flower weight (0.83 g), total chlorophyll (1.54 mg g-1), carbohydrates (6.38%), nitrogen (1.65%), phosphorus (0.37%), and potassium (1.79%). Similarly, CPPU application markedly enhanced plant performance. The concentration of 8 mg L-1 provided the highest plant height (36.91 cm), flower number (7.35 plant-1), fresh flower weight (0.87 g), total chlorophyll (1.48 mg g-1), and nitrogen (1.66%), while 12 mg L-1 resulted in superior branch number (6.69 plant-1), flower diameter (6.53 cm), carbohydrate content (6.31%), phosphorus (0.34%), and potassium (1.78%). In conclusion, the combined use of humic acid and CPPU enhanced vegetative growth, flowering performance, and biochemical composition of marigold, with the highest doses (4 mL L-1 HA and 8 - 12 mg L-1 CPPU) showing the most beneficial effects. These findings highlight the potential of HA and CPPU as effective biostimulant and growth regulator strategies for improving ornamental plant production.