Understanding plant growth and morphological changes during the growing season is important for identifying optimal harvest management practices for bioenergy grasses. Research was conducted at the University of Florida Plant Science Research and Education Center during 2010 to quantify monthly changes in characteristics that influence biomass quantity and composition of ‘L79-1002’ energycane (Saccharum spp.),  ‘Merkeron’ elephantgrass (Pennisetum purpureum Schum.), and a breeder’s line of elephantgrass called Schank. Canopy height, dry tiller mass, tiller density, leaf/stem ratio, leaf area index (LAI), and shoot dry matter (DM) concentration were quantified beginning in early June and every 28 d thereafter until December. Canopy height of Merkeron (3.6 m) and Schank (4.3 m) increased until November, but energycane height changed little after September (3.7 m). Energycane and Merkeron tiller mass reached a maximum in September, but Schank tillers continued to accumulate mass until October. In October, dry tiller mass was greatest for Schank (279 g), intermediate for Merkeron (197 g), and least for energycane (158 g). Tiller density was greatest in June and decreased for all grasses until September after which it remained relatively constant at 24, 19, and 16 tillers m^-1 of row for energycane, Merkeron, and Schank, respectively. Leaf/stem ratio decreased from June through November for all grasses, and Schank had the lowest ratio throughout most of the season, reaching 0.23 in November. Elephantgrasses reached maximum LAI in late June (Schank, 6.2; Merkeron, 6.1) but energycane reached a maximum of 5.1 in July.The LAI of all grasses decreased nearly linearly from September through the end of the growing season. All grasses increased DM concentration from June (avg. 139 g kg^-1) through October (avg. 325 g kg^-1). Energycane shoots were slightly lower in DM concentration during the middle of the growing season, but in general there was little difference among genotypes. Based on the growth and morphological characteristics observed, the breeder’s line Schank has excellent growth potential and is capable of utilizing the full growing season to accumulate biomass in this environment.