Perennial. Hardy in zones 3-9.
Start inside 8-10 weeks before planting out, as germination can be slow. Sow seed on the surface and prechill in the refrigerator for 5 days. Bring containers out and provide light and a soil warmth of 24°C (75°F). Seedlings are very delicate. Water gently and keep out of hot, midday sun. Transplant outside after last frost, 6-18" apart. Provide part shade if summers are hot. Will tolerate full sun if summers are cool and they have constant moisture. Deadhead regularly. Often self-seeds.