|Vigorous, clumping perennial with upright stems and coarse, hairy, dark green leaves up to 10 inches long. Bears forked cymes of violet, pink or yellow flowers. Bocking is a sterile cultivar that is not as invasive as the species and has white leaf margins. Plant 2 to 3 feet apart in rich soil. Comfrey contains protein and an impressive list of vitamins, but may cause severe stomach irritation if ingested. Remove flower stalks to keep flower production high.