Influence of willow bark extracts and application times on the production of Roselle

Roselle is an herbaceous perennial and short-day plant widely recognized for its medicinal properties. It is primarily cultivated for its fiber and, more notably, for calyx production. Given its importance, an experiment was conducted to examine the effect of willow bark extracts and their application timings on the growth and yield of roselle. The study was carried out at the Ornamental Horticultural Nursery, The University of Agriculture, Peshawar, Pakistan, using a randomized complete block design with a split-plot arrangement. The experiment consisted of two factors: Factor A, the time of application (20, 40, and 60 days after transplantation), assigned to the main plot; and Factor B, concentrations of willow bark extract (0%, 2%, 4%, 6%, and 8%), assigned to the subplot. In total, 15 treatments were evaluated, each treatment replicated three times. The results revealed that plants treated with 8% willow bark extract exhibited the best performance, recording the least days to flowering (139.26), the highest chlorophyll content (45.60), maximum leaf area (143.88 cm²), the greatest number of branches (21.11), the highest number of calyces per plant (64.55), calyx yield (4096.11 kg ha⁻¹), and seed yield (2302.56 kg ha⁻¹). The effects of 8% extract were statistically similar to those of 6% extract in most cases. Furthermore, spraying willow bark extract at 60 days after transplantation resulted in a significant increase in the number of calyces per plant (62.73) and seed yield (2285.87 kg ha⁻¹).