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. Prickly comfrey has pink and blue flowers while Quaker comfrey has blue, purple, or red-purple flowers.
Seed production is rare, and crops are usually established from root cuttings and crown divisions.
Vegetative growth does not cease with the start of flowering, and the plant will add new stems continuously during the growing season. The plant will grow rapidly after harvest and flower again. Comfrey crowns and roots are very winterhardy in northern Midwestern environments. Comfrey produces the highest yields in full sunlight and under cooler conditions. Unlike annual crops, the leaves do not readily wilt during extended periods of drought due to its deep root system.