Effects of Companion Cropping Ratios of French Marigold on Substrate Properties and Vegetative Growth of Hot Pepper in Urban Rooftop Agriculture

This study aimed to assess the impact of companion cropping ratios of hot pepper (Capsicum annuum L.) and marigold (Tagetes patula L.) on the physicochemical properties of the cocopeat-based substrate and plant growth characteristics in urban rooftop agriculture. Five cropping ratios were tested: pepper monoculture (PC), three companion cropping ratios (P2M1, P1M1, and P1M2), and marigold monoculture (MC). Overall, among the companion cropping treatments (P2M1, P1M1, and P1M2), P2M1 maintained more stable traits than the monoculture treatments especially; aside from pH, however, no significant differences were observed between treatments as the growth stage progressed. Pepper plants under the P2M1 ratio exhibited significantly greater leaf length and width than all other treatments (p < 0.05), but there was no significant difference in number of leaves. Marigolds in the P2M1 treatment also showed significantly higher growth parameters compared to P1M1, P1M2, and MC treatments (p < 0.05). Number of fruits and shoot dry weight were highest in the P2M1 treatment, while the root fresh weight peaked in P1M2. These results suggest that companion cropping with marigold, an aromatic ornamental plant, was mainly linked to greater stability of the substrate and to potential growth optimization of pepper plants.