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Botanical name: Rehmannia glutinosa
Common name: Rehmannia root, Chinese foxglove
Literal name translation: unprepared earth yellow
Family: Scrophulariaceae, figwort family
Part used in Chinese medicine: root
Major Chinese medicine actions:
Nourishes yin, generates fluids, clears heat, cools blood
Though they are not related, Rehmannia is sometimes called Chinese foxglove because of the similarity of the plant and its flowers to European common foxglove (Digitalis purpurea). In comparison, Rehmannia glutinosa is a somewhat smaller plant, with hairy leaves, and fewer flowers. It is native to northern China and Korea, growing on hillsides and waste areas, along highways and cracks in city walls.
Though they have been prolific in the wild, in recent times, most all Rehmannia is harvested from cultivated plants. The rootstock of vigorous plants found in the wild is dug up, cut into 1-2 inch lengths, and replanted in prepared beds. In mid-autumn, the roots are dug and buried in sand until the next spring. In April or May the roots are dug once again, cut into about 2 inch pieces and planted in permanent beds.
Growing and Propagation
The plant is hardy to USDA zone 9, about -13 degrees F, if the plants stay dry. The leaves are covered with soft hairs that make the plant susceptible to rot in warm damp winters, so in these climates, they are often grown in a greenhouse. The plants grow 6-12 inches high, preferring a warm sunny location in sun to partial shade and soil that is loamy, and moist but well drained. Flowers bloom from April to June, seeds ripen from May to July, and the roots should be harvested in November.
When propagating by seed, it should be sown in autumn or spring in a greenhouse. When seedlings are large enough to handle they can be potted and grown for at least their first winter in a greenhouse. They can then be planted out in late spring or early summer. Suckers and flower buds should be removed, leaving only one main stalk to grow.
Harvesting and Preparation
Rehmannia may be used fresh (Xian Sheng Di), dried (Sheng Di), or prepared (Shu Di). After harvesting the roots, they may be used fresh for up to three months. In this case, they are stored in dry mud and then dug up, cleaned and sliced as needed for use in decoctions. For Sheng Di, or dried rehmannia, they are sliced and dried immediately after harvesting.
For medicinal use, good quality Sheng Di consists of fat roots with a thin outer bark and a black shiny cross section. The roots should be large, thick and heavy.