Comfrey, like most green vegetables, is deficient in methionine and is also low in phenylalanine. Three ounces of dried turnip greens or spinach, in comparison to 20 oz of dried comfrey, supply adults with the total daily requirement of all essential amino acids, except for methionine. Comfrey also tends to have high ash content. Comfrey begins growth in early-April and by early May compact clusters of young leaves are visible in the crown of the old plant. Within a few weeks, the leaf blades with long petioles have grown to over 12 in.
Basal leaves are large, lance-shaped, stalked, and coarsely hairy.
The stem elongates rapidly and reaches a height of over 3 ft. Upper leaves do not have long petioles and are attached closely to the stem. Flowering starts in late May or early June and continues until fall. Leaves on flowering, erect stems are sessile or decurrent, and decrease in size up the stem. Flowers of common comfrey are usually creamy yellow, but white, red, or purple types have been found in Europe.