Regularly mown road verges are an important habitat for conservation of grassland vegetation. Disturbance and movement of seed-contaminated soil during road construction and maintenance makes road verges susceptible to the establishment of invasive alien plants such as garden lupine (Lupinus polyphyllus Lindl.). To combat the spread of L. polyphyllus via seeds, we tested methods for seed destruction using heat. This study aimed at developing heat eradication methods for dry and imbibed L. polyphyllus seeds applying dry heat (88, 93, 98, 103 C for 1, 3, 5, 10 min) in a laboratory, steam (85, 90, 95 C for 3, 5, 10 min) in a test box steaming device, and (97 C at 10 to 17 min; dry seeds only) in a stationary soil-steaming machine (S30). To speed up water absorption and posttreatment germination, the imbibed seeds were manually scarified before the heat treatment and the dry seeds afterward. Additionally, germination of two seed batches of different ages was tested applying dry heat (88, 98 C at 3, 5 min). Steam treatments inhibited seed germination more than dry heat in both dry and imbibed seeds. Germination dropped to <5% when steamed at ≥90 C or dry heated at >100 C. Seed germination decreased with higher temperatures and longer exposure times. Imbibed seeds exhibited lower germination compared with dry seeds for dry and steam heat. Approximately 0.5% of dry seeds germinated when steamed using the S30. The seeds collected in 2022 were less sensitive to dry heat than seeds from 2020. In conclusion, hot steam is more effective in reducing L. polyphyllus seed germination than dry heat. Thus, to successfully eradicate L. polyphyllus seeds in soil masses, we recommend steaming them at 97 C for at least 10 min.