Switchgrass (Panicum virgatum L.), a native of the North American prairies, has been selected for bioenergy research. With a focus on biomass yield improvement, this study aim (i) to estimate the genetic variation in biomass yield and important agronomic traits in ‘Alamo’, (ii) to determine correlations between biomass yield and agronomic traits, and (iii) to compare efficiency of phenotypic selection from a sward plot and advanced cycle half-sibs (ACHS) on the basis of space-plant performance. Sixty-two Alamo half-sib families (AHS) from a 4-yr-old Alamo sward and 20 advanced cycle half-sib families (ACHS) were evaluated in replicated field trials under simulated swards in Knoxville and Crossville, TN. Results showed significant variation (P < 0.05) among AHS for biomass yield, tillering ability, and spring vigor, suggesting the importance of additive genetic variation in these traits. Overall mean biomass yield of AHS was not different from the Alamo control, demonstrating the inefficiency of phenotypic selection from swards. Mean biomass yield of ACHS was 15 and 20% less than that of the control and AHS, respectively. Such results could be attributable to the influence of environment and genotype × environment interaction. However, results showed great potential for biomass yield improvement through selection on the basis of family performance. Using 10% selection intensity, parental control of two, and a narrow-sense heritability estimate of 0.11, gain per cycle selection from half-sib family selection is estimated to be 23%. Spring vigor showed potential use for indirect selection due to its high genetic correlation (rG = 0.75) with biomass yield. However, it is impeded by the low heritability estimate (h2 = 0.34).