Smooth brome (Bromus inermis Leyss.) has been planted widely for use as a forage grass and erosion control. Its competitive nature and rapid growth have allowed smooth brome to become an invasive species throughout the Northern Great Plains. Prescribed burning is commonly employed to control smooth brome in the region's remaining native grasslands. Burning at the initiation of elongation, when smooth brome populations are most vulnerable, destroys the carbohydrate reserves that allow the plants to recover. Identifying the five-leaf stage in phenological development has been recommended to signal the start of elongation in order to time prescribed burning to be most detrimental to smooth brome. Unfortunately, in a recent field survey of 27 sites in the Northern Great Plains, less than 1% of smooth brome tillers were observed to achieve the five-leaf stage prior to elongation, calling the tying of prescribed burning to identification of the five-leaf developmental stage into question. Accumulated growing degree days (AGDD) provides a more reliable indicator of smooth brome's vulnerability to control efforts through prescribed burning than reliance on the observance of the five-leaf stage. This study was designed to monitor phenological development of smooth brome in a controlled greenhouse environment to determine whether the correlation between AGDD and phenological development was exhibited in greenhouse populations across a gradient of nitrogen conditions encountered throughout the Northern Great Plains. It was determined that, while nitrogen treatment did affect the biomass and number of tillers produced, it did not affect the phenological progression of development. The greenhouse population reached 50% elongation at an average of 2287 AGDD.