The floral stems of genepi (Artemisia umbelliformis Lam.) are mainly used to produce liquors. Commercial cultures showed great variations in essential oil (aromatic compounds) and costunolide (bitter compound) contents. From 2001 to 2003, the incidence of the phenological stage on the quality of floral trusses of white genepi (Artemisia umbelliformis Lam.) was precisely defined. The ideal harvesting period for a maximal content of essential oil and costunolide, is the beginning of flowering. After this stage, the essential oil and costunolide contents dropped of about 50%. Nevertheless the chemical composition of the essential oil remained stable during the whole flowering period of white genepi.