ORGHPS Germination Guide: Sow @ 20°C. Seed germinates within 3 months Requires scarification. Nick or rub between sheets of sandpaper. Requires soaking. Place in warm water until seeds swell, usually 24-48 hours. Discard water and any seeds that remain floating. * tiny seed should be scarified with sandpaper or try soaking in boiling water to penetrate seed coat

Source: Ontario Rock Garden & Hardy Plant Society