Seeds from different populations of the same species often show distinct germination responses to the smoke-derived chemical karrikinolide (KAR1), thus limiting its potential for use in weed management. Gorecki et al. study the effect of the environment during seed development (i.e. the parental envioronment) on the KAR1-response of seeds from different populations of Brassica tournefortii and find that variation in response is reduced when parent plants are grown under the same conditions. Seeds from plants grown under drought stress are more responsive to KAR1 than seeds from well-watered plants. The parental environment is thus one of the key drivers of the KAR1-responses of seeds.