Fermi, This is a picture I took in April 2011 of one of several seed-grown Centaurea bella (from Turkey), which we'd planted I think the year before in our dry hot garden in southern Greece. Since planting they've never been watered, and thrive, flowering for the first few months each year. They stay in leaf all year, getting rather more silvery-leafed in summer then greening as soon as it rains in autumn. But they've never self-sown seedlings, rather to our surprise.