The present paper deals with the effect of a concentrated, depotassified,Beta vulgarisL. vinasse [desugared beet molasses, 3.5% nitrogen (N),2%sodium (Na)] on germination and growth ofHelianthus annuusL. Compared to other species [Lepidium sativumL.,Sorghum vulgarePers.,Lolium multiflorumLam.,Triticum aestivumL.,Hordeum vulgareL.,Medicago sativaL. and a wildMelilotus segetalis(Brot.) Ser.], sunflower, and ryegrass, had the smallestin vitrogermination indices under both solutions of 0.15 and 0.50% of pure vinasse. However, seedling emergence, plantlet growth, and nutrient content of sunflower grown in pots, in three different soil types, were not negatively affected by the application of a moderate dose of pure vinasse (roughly equivalent to 2–3 t ha‐1) at sowing or 30 days before. In a field experiment, the application of a similar dose of vinasse did not have any detrimental effects on sunflower growth, with the achenes reaching similar oil and fatty acid contents under both vinasse treatments (application at sowing and 30 days before) and control. The application of vinasse at sowing can partially avoid losses of N that can take place if the vinasse is applied too far in advance of sowing.