The relationships between dynamics and plasticity (ability of a hybrid to modulate its traits according to growing conditions) of agronomic and nutritional traits are unclear. Quantifying and characterizing these relationships can improve understanding of plant response mechanisms to growing conditions in short cropping periods at high latitudes. This study investigated the dynamics of key agronomic performance and forage quality traits and the importance of their mean values for expression of plasticity. Data were collected on eight sampling occasions during the cropping period in 2013 and 2014, using six phenologically different forage maize hybrids grown at three high-latitude locations. The dynamics of all traits studies were significantly affected by hybrid and environment (combination of location and year). Dry matter yield (DMY) and dry matter content (DM) were affected by interactions between hybrid, growing conditions on each sampling occasion, and overall growing conditions in the different environments. Neutral detergent fiber digestibility (NDFD), starch (STA) concentration, water-soluble carbohydrate (WSC) concentration, and organic matter digestibility (OMD) in the hybrids differed significantly over time across the environments. Early-maturing hybrids progressed faster in maturity based on DM content and had higher STA concentration, NDFD, and OMD at a given time than later-maturing hybrids. Similar DMY and higher NDFD and OMD in early-maturing compared with later-maturing hybrids, regardless of sampling occasion or environment, suggests that use of early-maturing hybrids is advantageous in the short cropping season at high latitudes. For most traits, plastic ability [plasticity of trait x/mean value of trait x, or ability to change expression of plasticity of a trait is based on the mean value of the trait] was dependent on the mean value of a trait and declined with increasing mean value. Plastic ability of DM, DMY and STA was higher at early developmental stages and decreased at later developmental stages, but the opposite was true for WSC and CP. Although the dynamics of trait development over time differed between the hybrids, the dynamics of plastic ability for four traits (DM, WSC, OMD, NDF) were similar in all hybrids. These maturity characteristics-based responses of the six hybrids in terms of trait dynamics and plastic ability, and the dependence of plastic ability on the dynamics of corresponding trait, can potentially be exploited in development of new variety/hybrid and prediction models for further improving the agronomic and nutritional value of forage maize crops at high latitudes.