Comfrey is a favourite of the vegetable gardener, not as a source of food but, to produce plant fertiliser. Comfrey is also believed to work as a herbal medicine for various ailments. It is a very vigorous plant that can last for 20+ years and will grow in most soils (except very chalky soils). It grows best in moist soils and will do well in full sun or partial shade.
You can buy and grow comfrey from seed or plants. If sowing from seed, sow in deep pots or root trainers. Plant out in spring or early summer when days are warm. Keep watered until established.
Give the plants time to establish (1-2years). Then harvest whenever there is a good crop of leaves. Cut leaves right back and use in the compost bin, shredded as a mulch, or make comfrey tea (liquid plant food).