Nine maize hybrids, representing early, medium and late maturities (maximum 3000 corn heat units), were grown at 75 000 and 100 000 plants/ha for 2 yr at two locations in order to examine the in vitro digestible dry matter (DDM) yield and quality of whole-plant (shoot) and stover components. Early hybrids produced 90% as much DDM yield as medium or late hybrids. Comparing densities, the higher density resulted in a greater increase in DDM yield at Surrey than at Agassiz and it did not depress whole-plant dry matter (DM) content. Whole-plant DM digestibility (DMD) was 2% lower for early hybrids compared to mediums or lates. Density had no influence on whole-plant DMD at Surrey, but the higher density reduced it by 1% at Agassiz. Stover DDM yield was greater at Surrey than at Agassiz whereas whole-plant DDM yield was greater at Agassiz. Harvest index was positively, but not closely, correlated with whole-plant DMD (r = 0.28***) and was inversely correlated with stover DMD (r = − 0.45***). Thus, nutritive value of maize was only marginally dependent on the grain component. Results suggest that, in the marginal corn-growing environments of the region studied, it may be beneficial to use hybrids considerably later than those normally adapted and grow them at a density approaching 100 000 plants/ha to maximize digestible yields and quality. The harvested forage may have a DM content too low for direct ensiling, but this can be rectified by addition of dry high-protein supplements (e.g. alfalfa cubes) at ensiling time.