In the cooler regions of the world, the area under forage maize (Zea mays L.) production has increased, and breeding for digestibility has gained importance. This study was conducted on digestibility traits of stover in maize forage, to determine variation, as analyzed by the combining‐ability approach, and correlation coefficients (r) in these traits and r between these and dry matter (DM) yield traits. Diallel crosses among 12 inbred lines were evaluated at silage and grain harvests for 2 yr at two agro‐climatically diverse locations in West Germany. Stover samples were analyzed for in vitro digestible organic matter (IVDOM), neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent lignin (ADL) using laboratory and near infrared reflectance spectroscopy (NIKS) methods. Mean squares due to general (GCA) and specific combining ability (SCA) and their interactions with environments (GCA ✕ E, SCA ✕ E) were, for the most part, significant. At silage harvest, GCA was the most important source of variation in all traits, followed by SCA ✕ E interactions. At grain harvest, GCA and SCA ✕ E for IVDOM and ADL and SCA ✕ E for NDF and ADF accounted for larger variability than SCA and GCA ✕ E. The genetic ratio indicating the relative importance of GCA vs. SCA was > 0.81 in all cases, except that it ranged from 0.40 to 0.58 for NDF and ADF at grain harvest. The IVDOM had negative r with NDF, ADF, and ADL, and r values were stronger at silage harvest; IVDOM was not correlated with stover DM yield, and had negative r with ear DM yield. The results showed significant genotypic variation for several traits, with GCA the most important source of variation for most traits, and showed that selection for digestibility should preferably be made at the ensiling stage.