Rehmannia glutinosa, commonly known as Chinese foxglove, is a perennial herb native to regions such as Henan, Shanxi, and Hebei in China. It is widely cultivated for its medicinal roots and herbs, which are processed into different forms—fresh, dried, or steamed—each offering distinct therapeutic properties. The plant has a sweet and bitter taste, is cold in nature, and possesses the ability to clear heat, nourish yin, cool the blood, moisten dryness, and regulate menstrual cycles. It is traditionally used to treat conditions like yin deficiency fever, blood stasis, irregular menstruation, fetal instability, and constipation due to yin deficiency.
**Introduction to Plant Characteristics and Varieties**
The plant typically grows to a height of 0.2–0.4 meters. Its roots are fleshy, thick, and cylindrical or spindle-shaped, while the basal leaves are obovate or oblong. The stems are erect, often bearing one to three flowers, with purple-red or yellowish blooms. The fruit is an ovoid capsule containing numerous small seeds.
There are several popular cultivars, including 'Golden Champion', 'Black Eagle', 'White Crocodile', 'Sweet Potato King', 'Guoli Cat', and 'Dqingying'. Additionally, hybrid varieties like Beijing No. 1 and Beijing No. 2 are also widely cultivated in certain regions.
**Biological Characteristics**
Rehmannia glutinosa thrives in temperate climates and exhibits specific growth patterns. It is usually planted in spring, with the main vegetative growth occurring in the early stages. After about eight months, the root system becomes more developed than the above-ground parts. The plant dies back after frost, surviving the winter without flowering. In the following spring, it regenerates and flowers fully.
The plant prefers well-drained sandy loam soil that is slightly acidic to alkaline, rich in organic matter, and receives ample sunlight. It requires moderate moisture during the root expansion phase (August–September) and can tolerate cold temperatures. However, it needs consistent warmth for optimal growth.
**Cultivation Techniques**
1. **Site Selection and Preparation**: Choose flat, sunny, and well-drained fields with fertile soil. Avoid areas where peanuts, beans, or sesame were previously grown. Deep plowing (25–30 cm) is recommended before planting. Raised beds are ideal in high-rainfall areas, while wide ridges are suitable for arid regions.
2. **Propagation Methods**: The primary method of propagation is through root cuttings. Root sections measuring 5–6 cm in length, with a diameter of 0.8–1.2 cm, are planted when the average daily temperature reaches 13°C. The planting period varies by region: mid-April in Beijing, March in Chongqing, and early spring to late December in Henan. A spacing of 33 cm between rows and 15–20 cm between plants is standard. For thin soils, higher plant density is recommended. Alternatively, shoot propagation can be used, where young shoots are taken from the mother plant and immediately replanted.
3. **Field Management**: Regular weeding and removal of buds are essential. Fertilization with bean cake or ammonium sulfate is advised one month after emergence. Watering should be moderate, maintaining a "yellow grass" condition. Irrigation should follow fertilization, avoid overwatering, and be avoided during extreme heat or rain.
4. **Pest and Disease Control**: Common issues include yellow leaf spot, yellow wilt, soybean cyst nematode, and cotton red spider mites. Prevention includes crop rotation, using disease-free seeds, and proper irrigation. Fungicides like chlorothalonil or Bordeaux mixture are effective against leaf spots. Nematodes can be controlled through soil disinfection and avoiding continuous cropping. Spider mites are managed using insecticidal sprays like amifenthrin or amitraz.
**Harvesting and Processing**
Rehmannia is typically harvested between September and October. After digging up the roots, they are cleaned and dried. Fresh roots are then steamed and slowly baked until they turn black and become soft. Once cooled, the outer skin is removed, and the roots are left to rest for 1–2 days before final drying. To enhance its medicinal properties, raw roots are soaked in 50% rice wine, sealed, and steamed in a water bath until the wine is absorbed. Finally, the roots are sun-dried until slightly moist.
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