Root variation has become an important target for geneticists, ecologists, and breeders, given its direct influence on plant adaptation, resilience to climate change, and biomass and seed yields. However, the underground nature of roots has limited the assessment of root variability in plant species. In this study, we evaluated several root traits in a sample of distinct yellow lupin accessions grown under cold conditions and at three time points. Analyses of variance showed a highly significant accession (genotype) effect on primary root length (PRL), primary root area (PRA), and total root area (TRA), indicating that at least part of the root variation was explained by a genetic component. Significant accession*time interactions for PRL and PRA suggested that root growth rates (assessed using these traits) may change over time across genotypes; however, a more extensive study including a larger number of accessions and growing times must be conducted to confirm this finding. Differences among L. luteus accessions in PRL, PRA and TRA suggest the existence of favorable variation in plantlet root traits and the possibility of breeding stronger and better-established yellow lupin plants when grown under cold conditions.