The effect of cold stratification on seeds of Erysimum cheiranthoides L., a late germinating summer annual in Sweden, was studied. Seeds were stratified in darkness on filter paper, either at +3░C or under natural temperatures outdoors and were tested for germination at regular intervals during ten months. Cold stratification reduced dormancy, but full germination was not achieved, nor did seeds gain the ability to germinate at low temperatures. Dormancy increased when seeds were subjected to summer temperatures. The combination of a requirement for cold stratification and warm germination temperature ensures that Erysimum cheiranthoides does not germinate in the autumn in cold temperate climates, and that substantial germination commence in late spring when soil temperatures increase. This germination phenology pattern was confirmed in a parallel experiment with seeds sown outdoors.