Switchgrass (Panicum virgatum L.), a warm-season grass, grows most rapidly in mid-summer when cool-season species such as tall fescue (Festuca arundinacea Schreb.) may have limited growth due to high temperature and low soil moisture availability. The objectives of this study were to investigate physiological factors and to determine management strategies that could optimize growth of switchgrass. The influences of two successive drought cycles on performance and water relation parameters of switchgrass and tall fescue were studied in growth chamber conditions. Water was withheld from conditioned plants until elongation of tillers stopped. Then pots were rewatered and a new drought cycle followed. Control plants remained well watered during this time. Both conditioned and control plants were then subjected to a challenge water stress. Total leaf elongation and soil water content (SWC) were measured daily. Leaf water potential (Ψ), osmotic potential (Π), relative water content, and concentrations of K, Na, Ca, and total free sugars were measured at the end of each water-stress cycle. Osmotic potential at full turgor (Π₁₀₀), symplastic water content (SYM) , and modulus of elasticity (∊) were determined from pressure-volume curves at the end of the two conditioning cycles. Conditioned plants of both species elongated more during the challenge water-stress than control plants and had lower SWC and Ψ when their leaf elongation ceased. Conditioned plants exhibited osmotic adjustment, accumulating free sugars and K, as a result of drought stress. Switchgrass SYM did not change, while Π₁₀₀ decreased, suggesting active salt accumulation. Increased ∊ somewhat counteracted the beneficial influence of osmotic adjustment. Tall fescue SYM increased, while Π₁₀₀ did not change. Decreased ∊ improved drought tolerance of tall fescue. Field experiments were conducted to investigate the influence of date of first harvest and cutting height on yield distribution and canopy characteristics of ‘Pathfinder’ (2-yr study), ‘Cave-in-rock’, and ‘Blackwell’ (1-yr study) switchgrass. Seasonal distribution of dry matter production was established by measuring first-harvest yields and regrowth. The canopy of Pathfinder was characterized by determining number and weight of tillers, light penetration, leafiness, specific leaf weight, and leaf area index in profiles of the canopy before harvest and in regrowth. First-harvest yields increased as date of first cut was delayed and cutting height was lowered. Cutting at 20 cm decreased the yield of first cutting in a second growing season. Plots not harvested in the first growing season gave higher yields in the second growing season compared with previously harvested plots, suggesting that any harvest may decrease subsequent yield potential. Regrowth decreased as date of first cut was delayed. A cutting height of 30 cm produced greater regrowth than cutting at 20 cm. Yields and canopy characteristics suggest that removal of growing points decreased second-harvest yields and weakened regrowth potential in the following year. To maximize regrowth to be used for grazing during July and August, switchgrass hay should be cut after 10 June and before 21 June. / Ph. D.