New plants should be planted each year. The entire plant should be harvested and removed its second year before flowering begins. Once flowering begins, very little usable foliage is produced. The plant's energy is focused on flowering and seed production. Perennial herbs should be given a permanent location in the garden where they can grow undisturbed year after year.
Perennial herbs require periodic division to remain healthy and productive.
Divide perennial herbs when they show decline, become woody or overgrown, or when you want new starts. Improving soil drainage and mulching after the soil freezes to prevent heaving will increase winter survival.