Karrikinolide (KAR1) is a smoke-derived chemical that can trigger seeds to germinate, and shows promise as a tool for flushing out weed seeds from the soil seed bank. Long et al. demonstrate that weeds of Brassicaceae are particularly responsive to KAR1, and that these responses are complex and transient: light and temperature conditions, dormancy state and seed lot all influence sensitivity to KAR1, and a response to KAR1 can be induced. Three ‘response-types’ are proposed for assessing the effects of KAR1 on seeds: inherent, inducible and undetected. All 15 seed lots in this study fall into the first two categories, so KAR1 has a clear potential for managing weeds of Brassicaceae.