Ground‐cover assessments of grassland swards provide information on durability and persistence, which in turn relate to disease resistance and competitive ability. These assessments are traditionally performed visually, but digital imaging can provide a more accurate method of ground‐cover scoring. Differences in ground cover between late‐heading perennial ryegrass (Lolium perenne L.) cultivars in four trials (2 yr of sowing and two sites) were determined using both digital imaging and visual scoring. Ground‐cover percentages were calculated from digital images with public‐domain software on the basis of color separation of grass leaves from bare soil. For both years of sowing, highly significant interactions of cultivar and site were detected. Significant differences between cultivars were detected in three out of four trials, with diploid cultivars having greater cover than tetraploids in the older trials. Thus digital image analysis of ground cover may be a useful tool in crop improvement and provision of guidelines regarding suitability of a particular cultivar for a particular site.