Technical Abstract: Harvest management of switchgrass grown for biofuel must consider not only biomass yield, but also the fuel quality of the biomass. A 3-yr study was conducted to determine the effect of fall vs. spring harvest on biomass yield and biofuel quality. In winter with low snowfall, delaying harvest from fall to spring did not affect yield. However, in winters with above average snowfall, biomass loses were 40%. About 25% of the yield reduction during winter resulted from loses in tiller weight with reductions in leaves and the panicles; however, 75% of the yield reduction was due to biomass not picked up by the baler. Although the yield is highest in late summer, mineral element concentration in the biomass decrease after the peak yield through a killing frost and into spring, thereby enhancing biomass quality for combustion. Although the biomass yield decreased over the winter, energy yield from gasification did not decrease on a unit biomass basis, whereas ethanol production decreased about 25%. Switchgrass moisture content needs to be less than 15% for storage but averaged 34% in the fall vs.7% in the spring. Although there was substantial reduction in switchgrass yield with spring harvest, the biofuel quality of spring harvested biomass was greater than fall biomass.