Performance of Five Cool-Season Turfgrass Cultivars for Fall Overseeding of Bermudagrass in Mediterranean Climate

Autumn overseeding with cool-season turfgrass species is a widely adopted practice under Mediterranean climatic conditions to mitigate winter dormancy and loss of green color in bermudagrass (Cynodon dactylon). This study evaluated, over two consecutive winter seasons (2022–2023 and 2023–2024), the performance of five cool-season turfgrass cultivars used for autumn overseeding on bermudagrass (‘Arden 15’) in Valencia, eastern Spain. The cultivars included Lolium multiflorum ‘Upstart’, Lolium perenne ‘CT7’ and ‘Sirtaky’, Poa pratensis ‘Liberator’, and Poa trivialis ‘Dasas’. Turf performance was assessed weekly from December to April using visual green color ratings, normalized difference vegetation index (NDVI) measured with two hand-held sensors (GreenSeeker and CropCircle), and normalized difference red edge index (NDRE). The area under the progress curve (AUPC) was calculated as an integrative indicator of turf performance over time. Winter temperature differences significantly influenced bermudagrass dormancy duration and overseeding response. Among the evaluated cultivars, ‘CT7’ consistently showed the highest winter greenness and vigor but exhibited a darker green color than bermudagrass, potentially reducing visual uniformity. The L. perenne ‘Sirtaky’ and P. pratensis ‘Liberator’ cultivars provided a closer chromatic match, although ‘Liberator’ established more slowly. The NDVI and NDRE measurements supported the visual assessments, though correlations between sensors varied among cultivars and seasons, with the GreenSeeker sensor detecting larger cultivar differences than the CropCircle sensor, particularly during colder winters. In addition, the AUPC proved to be an effective integrative metric for comparing cultivar performance over a defined period. Overall, overseeding effectively reduced winter discoloration of bermudagrass, with ‘Sirtaky’ emerging as the most balanced option for Mediterranean sports overseeding management on C. dactylon (‘Arden 15’).