SUMMARYThe nitrate content of seeds of the annualSisymbrium officinalewas raised by weekly nitrate fertilizations of the seeding mother plants. Nitrate content and germination of the seeds produced were positively correlated. Seed lots with different endogenous nitrate contents were buried at 10 cm in sandy loam. At regular intervals seeds were exhumed and germination was tested. Both the initial differences in endogenous nitrate content and the differences of germination rapidly diminished during burial because nitrate rapidly leached from the seeds. The sensitivity of exhumed seeds to applied nitrate strongly varied during this 1‐year study. Sensitivity to nitrate was low in December and had increased in January‐February probably because of low winter temperatures. A cold pretreatment in Petri dishes also strongly increased sensitivity to nitrate. Endogenous nitrate content of seeds collected in the field was much lower than reported in this study and therefore the differences in seed‐nitrate content in the field probably are of limited ecological significance. A high endogenous nitrate content will stimulate germination only temporarily. In contrast, the changes in sensitivity in nitrate seem ecologically important because they will restrict germination ofS. officinaleto seasons suitable for survival of the seed