In fields, the timing of weed emergence flushes is mostly related to the timing and rate of seed germination, which depend on soil temperature and water potential as well as soil tillage and crop sowing date. Base temperature and base water potential for seed germination are parameters required in weed dynamics models to take into account the effects of soil conditions on weed demography. Since these parameters are difficult to measure, our objective was to develop a method for estimating them from easily accessible information. Data on base temperature and base water potential for germination were collected from the literature for 28 weed species. Correlations were then searched for between these parameters and (i) the species ecological indicator values of Landolt and Ellenberg for temperature and moisture and (ii) dates of the onset and end of weed emergence based on experts’ knowledge. Both base temperature and base water potential for germination were partially correlated with the species indicator values found in the literature. These correlations explained however only a small proportion of the variance of base temperature and water potential. In contrast, the base temperature of spring-emerging species was highly correlated with the mean soil temperature at the mean onset date of each species’ spring emergence flush. Water potential for germination was higher for species requiring high base temperature. The date of spring emergence onset of a species, which can be easily assessed from experts’ knowledge, can thus be used to estimate their base temperature and then their base water potential for germination.