Seed germination partly depends on both base temperature (Tb) and base water potential (Ψb), which currently are known only for a small number of species. Laboratory experiments were conducted to estimate these parameters for 14 weed species using the ‘x-intercept’ method. Tb and Ψb (°C and MPa) for the 14 weed species were as follows: Amaranthus retroflexus (8.9 and −0.95), Ambrosia artemisiifolia (3.6 and −1.28), Avena fatua (2.2 and −1.02), Capsella bursa-pastoris (4.5 and −0.95), Chenopodium album (5.9 and −0.80), Echinochloa crus-galli (6.2 and −1.19), Geranium dissectum (0.6 and −3.31), Matricaria perforata (2.0 and −0.75), Picris echioides (5.2 and −0.79), Polygonum lapathifolium (5.8 and −1.55), Senecio vulgaris (2.5 and −1.23), Setaria pumila (8.6 and −0.75), Solanum nigrum (11.6 and −0.89) and Veronica hederifolia (0.2 and −1.67). The two parameters were used to determine potential germination times during expected non-dormancy periods for three contrasting climatic years in Dijon, France. The number of potential germination days varied little among the tested climatic years, but substantially among species, ranging from 95 ± 9 days for V. hederifolia to 280 ± 7 days for M. perforata. These results may be of value for development of predictive growth models and understanding times when weed control may be most feasible.