The field experiment was conducted at the Regional Agricultural Research Station, Pattambi of Kerala Agricultural University with the objective to understand the effect of seed treatment using different organic leaf extracts on the growth and yield of cowpea. The experimental design was used for the layout of the design in Randomized Block Design, with three replications and nine treatments. The experiment was conducted with 9 treatments viz., the 5% leaf extracts of Calotropis (T1), Pappaya (T2), Pongamia (T3), Castor (T4), Moringa (T5), Vitex (T6), Neem (T7), Tulsi (T8), Control with distilled water (T9). Different field observations revealed that the seed hardening significantly influenced the seed yield and yield contributing characters of cowpea. The highest yield was recorded due to seed hardening treatment with Pongamia 5% leaf extract (T3) for 4 hrs followed by Calotropis 5% leaf extract (T1) for 4 hrs. All the seed hardening treatments had significant effects on yield contributing characters like plant height at maturity, number of branches(primary and secondary) per plant, number of clusters per plant, number of seeds per pod, pod length, pod girth, pod weight, 100 seed weight, seed yield per plot(kg/ha) and dry matter production at harvest. The nodule count at flowering and total chlorophyll content at maturity were also found to be significantly different among the treatments. The seeds hardened with Pongamia leaf extract (5%) (T3) for 4 hrs recorded higher field emergence with maximum grain yield (716 Kg/ha), plant height at maturity (145.07 cm), number of primary branches per plant (3.60), seed yield per plant (g) (13.69 g), and seed yield (716 kg/ha) followed by Calotropis leaf extract (5%) (T1) for 4 hrs with a seed yield of 694 kg/ha.