Lignocellulosic biomass has the potential to be asignificant source of renewable energy, provided that current challenges regarding sufficient biomass production and efficient biomass conversion are met. Floral transition is a major developmental switch in the life of flowering plants which dictates whether photosynthetic products should be investedin vegetative growth or reproductive development. To directly evaluate the contribution of floral transition to biomass yield, we manipulated the onset of flowering in the model legume Medicago truncatula using a mutagenesis approach. Throughforward genetics screening ofTnt1-tagged mutants, we identified three M. truncatula lines altered in flowering time and fertility: a delayed flowering mutant named vernalization-insensitive delayed flowering in long days(vdf), a nonflowering stemless mutant named headless(hdl), and a male sterile mutant named medicago male sterile 1(mms1). Biomass yield analyses at different stages of development in these mutants revealed that the vdf mutant had the highest aboveground biomass and the hdl mutant had the lowest biomass at 70 days after germination.The difference in biomass yield between the vdf mutant and wild-type R108 became apparent after floral initiation and peaked at 90 days after germination, the late blooming stage for R108, where the vdf plants produced approximately twofold more biomass than R108. Interestingly, vdf, hdl, and mms1 mutants produced significantly less lignin than R108. Our results suggest that delaying floralinitiation could be employed as a convenient tool to simultaneously improve biomass quantity and quality, provided that this is achieved without pleiotropic developmental defects.