Plant stature, flowering time and ear set are related to maturity, disease and insect resistance, drought tolerance, root lodging and yield, which are all major trait targets for maize breeders. In an effort to understand the effects of year, location, and planting density on these traits, we grew the IBMRIL and IBMDH populations in high and low density at several locations in the cornbelt over a period of years. The effects of temperature, precipitation, and solar radiation at key crop growth phases were quantified for each trait using partial least squares regression. The heritability of each trait across high and low planting densities was estimated. Using composite interval mapping, we placed by- and across-environment and density QTL for these traits on a dense genetic map. The effects of environment and planting density on each of these traits were significant. Several QTL with very narrow confidence intervals and functions of interest to breeding programs were identified, and QTL were detected differentially across environments and planting densities. Use of phenotypic and genotypic selection for plant stature, flowering time, and ear set is discussed, and functional hypotheses for these QTL are explored in the context of previously identified QTL.