You can't get any easier to grow than Linaria purpurea. Slender spikes of tiny violet-blue snapdragon-like flowers over narrow, whorled, blue-grey leaves light up many an old garden. Blooms all Summer in full sun or part shade. Fairly drought tolerant once established and it reseeds! To 3’ high and 1’ wide, it looks smashing in groupings. Native to southeastern Europe.