Vitamin A dense Orange fleshed sweet potato (OFSP) has the potential to build resilient livelihoods against Vitamin A Deficiency (VAD), food insecurity, and climate change. However, the adoption of OFSP among smallholder farmers in Malawi remains low. Although many scholars across the globe have reviewed the seed systems of OFSP, no empirical study, in Malawi or elsewhere, has modelled how the use of the various sources of vines affect farmers’ seed security and eventual decisions to adopt biofortified OFSP varieties. The study employed a mixed methods approach and used a Triple Hurdle model to analyze the effect of the existing sources of vines on the adoption of OFSP among 721 randomly sampled households in central and northern Malawi. The study also developed a seed security experience score (SSES) in order to assess the capacity of the existing sources of vines to ensure farmers’ seed security. By defining adoption as a three-stage process, and by shifting the seed systems focus to capacity of the existing sources of vines, the study departs from the conventional approaches that most scholars have used to model adoption of OFSP. The study found that the existing sources of vines influenced all the three stages of adoption. The SSES results indicated that the capacity of the existing sources subjected the majority of the farmers to a highly seed insecurity status. Interventions therefore must be designed to address the seed security challenges associated with the existing sources in order to enhance the capacity of the sources for widespread and sustained adoption of OFSP.