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 & it reseeds! To 3’ high & 1’ wide, it looks smashing in groupings. Native to southeastern Europe.