Seed from selections of blue panicgrass, Panicum antidotale Retz, for heavy and light seed‐weight from six cycles of recurrent selection were evaluated for association between seed weight, seedling vigor, and several aspects of seedling energy metabolism. Seed and seedling fresh weight, respiration rate, free sugar levels, mitochondrial protein content, adenosine triphosphate (ATP), and total adenylate phosphates content were sampled after 0, 6, 12, 24, 36, 48, 60, and 72 hours of germination and initial growth. Dry weight of seed decreased about 2% during the first 72 hours of germination and fresh weight of all seedlings increased about 60% in 72 hours Respiration rates were higher for heavy seed‐weight selections through the first 72 hours Content of free sugar (mg per seed) was significantly greater for heavy seed‐weight selections. Pools for adenylate phosphates were larger for heavy seed‐weight selections on the basis of nmoles per seed. Energy charge values were not significantly different during germination; however, energy charge values for unimbibed seed were greater for heavy seed‐weight selections. Heavy seed contained more free sugars for respiratory substrate and more adenylate phosphates for further phosphorylation. The enhanced respiratory metabolism resulted in increased rates of ATP formation, and larger seedlings resulted.