SummaryGermination in the laboratory of seeds ofBarbarea strictaandB. vulgariswas inhibited by 20–200 mg l−1chlormequat chloride or daminozide. Seeds treated with chlormequat and then washed with water and kept on moist quartz sand remained dormant for up to 1 year, but dormancy could be broken at any time by treatment with gibberellic acid. Similar results were obtained withCapsella bursa‐pastorisandThlaspi arvense.In contrast, germination of other weed species, such asSpergula arvensisandMatrkaria perforata, took place in the presence of chlormequat and daminozide in concentrations of 5000–10000 mg 1−1. The relevance of the results to the duration of seed dormancy in the soil is