Evaluation of Culture Media for In Vitro Propagation of Hydrangea arborescens Based on Quantitative and Qualitative Assessment

Efficient propagation of Hydrangea arborescens is essential for the stable production of high-quality plantlets. However, propagation via stem cuttings is often limited by environmental conditions and inconsistent rooting. This study aimed to identify an effective in vitro culture medium by integrating quantitative growth traits with image-based quality analysis. Seven culture media (M1–M7), consisting of Murashige and Skoog (MS), McCown Woody Plant (McCown), and Gamborg B5 basal media supplemented with different plant growth regulator combinations, were evaluated based on shoot number, root number, plant height, and fresh weights, and plantlet quality was assessed using Green area, ExG (excess green index), and a composite z-score. Significant differences were observed among treatments. M5 and M7 produced the highest shoot numbers, and M7 showed the greatest fresh weight. Image-based analysis indicated that M2 and M7 exhibited the highest overall quality, whereas M3 showed the lowest performance. Basal media types did not significantly affect plantlet quality, whereas hormone treatments enhanced both shoot multiplication and callus formation. A positive association was observed between callus formation rate and shoot number (Spearman’s ρ = 0.74, p < 0.001). Overall, M7 (Gamborg B5 medium supplemented with 30 g∙L−1 sucrose, 1.5 mg∙L−1 BA, and 0.25 g∙L−1 gelrite) provided a balanced combination of high propagation efficiency and plantlet quality, and these findings contribute to the efficient production of high-quality planting materials.