S. officinale (comfrey)
Comfrey is a hardy perennial used to brew an herbal tea although regular use is not recommended, as it can cause liver damage. Farmers, especially in Europe, also grow comfrey for composting, plowing it back as an enrichment for the soil. It is a sturdy plant, reaching a height of 2 to 3 1/2 feet with very large, hairy lower leaves, as much as 15 to 20 inches long; the leaves grow smaller in size higher up the flower-bearing stem. Beginning in late spring, 3/4-inch-long well-shaped flowers of yellow, mauve, blue or white bloom in arched sprays on slender stems and keep blooming for most of the summer.
HOW TO GROW. Comfrey is hardy in Zones 3-10. It does best in full sun but tolerates partial shade; it thrives in any moist, fairly rich garden soil. It is usually grown from root divisions or from root cuttings taken in the spring or fall. Plant the root sections horizontally, 3 to 6 inches deep and 3 to 4 feet apart, away from smaller herbs. Once established, comfrey spreads aggressively and is hard to eradicate.