Optimizing the growth and flowering of Rosa hybrida L. (Roses) through synergistic light and biostimulant management

Abstract

BACKGROUND: Optimizing the growth and flowering of ornamental Roses is critical for improving horticultural productivity. This study investigated the synergistic effects of light intensity and two biostimulants, seaweed extract (SWE) and active dry yeast (ADY), on the growth, flower quality, chlorophyll, and essential nutrients content of rose plants. A factorial experiment tested three light regimes (full sun, 65% and 75% shading) combined with two concentrations of SWE (1000 and 2000 mg·L⁻¹) and two concentrations of ADY (3000 and 4000 mg·L⁻¹). RESULTS: Cultivation under shading (65% and 75%) consistently reduced vegetative growth and key nutrients elements, including the chlorophyll content (SPAD) and leaf concentrations of N, P, Zn, and Cu. The full-sun and 65% light conditions yielded the highest chlorophyll content, which were significantly greater than those of the 75% shade treatment. Nutrient analysis revealed that full sun maximized N, P, Zn, and Cu, whereas K was highest under 75% shade. Conversely, plants grown under full sun, when supplemented with biostimulants, presented significant and synergistic increases in growth, flower quality, and nutrient accumulation. The most effective treatment was the combination of full sun and 4000 mg·L⁻¹. This combination significantly optimized key horticultural traits and resulted in the highest N, Zn, and Cu levels. CONCLUSION: Overall, the findings indicate that the positive effects of biostimulants on roses depend strongly on light availability, supporting a sustainable strategy that integrates light management and biostimulants application to enhance commercial rose production.