Rehmannia glutinosa, commonly known as Chinese foxglove, is a perennial herb native to regions such as Henan, Shanxi, and Hebei in China. The plant's roots and herbs are processed in different ways, resulting in varieties like fresh Rehmannia, cooked Rehmannia, and stir-fried Rehmannia. It has a sweet and bitter taste, is cold in nature, and possesses properties that clear heat, nourish yin, cool the blood, moisten dryness, and regulate menstrual flow. It is widely used in traditional medicine to treat conditions such as yin deficiency fever, blood stasis, irregular menstruation, fetal movement disturbances, and constipation due to yin deficiency.
**Introduction to Plant Characteristics and Varieties**
1. **Plant Characteristics**: This herb typically grows to a height of 0.2–0.4 meters. Its roots are fleshy, thick, and cylindrical or spindle-shaped, with basal leaves that are obovate or oblong. The erect stems bear one to three flowers, often arranged in racemes, and display colors ranging from purple-red to yellowish. The fruit is an ovoid capsule containing numerous small seeds.
2. **Variety Profile**: There are several popular cultivars, including "Gold 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 cultivated in certain areas.
**Biological Characteristics**
1. **Growth and Development**: Rehmannia is usually planted in spring. The initial growth phase focuses on shoot development, and after about eight months, the root system becomes more prominent. After frost, the above-ground parts wither and go dormant through winter. These plants will flower in the following spring.
2. **Environmental Requirements**: The plant thrives in warmer conditions but is relatively cold-tolerant. During the early growth stage, soil moisture should be around 12% (indicated by yellow soil). In August and September, maintaining moderate soil moisture helps increase yield. The plant requires ample sunlight and prefers sandy loam soils that are slightly acidic to alkaline, loose, and fertile. Organic fertilizer is highly recommended for optimal growth.
**Cultivation Techniques**
1. **Site Selection and Preparation**: Choose flat, well-drained, sunny, and fertile land with good irrigation. Avoid planting in areas where peanuts, beans, or sesame were previously grown. Apply sufficient base fertilizer after autumn harvests, and plow to a depth of 25–30 cm. In high-rainfall areas, raised beds are preferred, with ridge distances of 33–78 cm and a height of 25 cm. In arid regions, ridges should be wider, around 130 cm.
2. **Propagation Methods**: The main method of propagation is through roots or shoots. Root propagation involves planting at an average daily temperature of 13°C, with the ideal planting period between March and June depending on the region. Select healthy, disease-free roots of 0.8–1.2 cm in diameter, cut into 5–6 cm sections, and plant them in rows spaced 33 cm apart. Cover with 3–4 cm of soil and compact it after watering. For shoot propagation, young shoots can be taken from the mother plant when they reach 7–12 cm in height and immediately planted.
3. **Field Management**: Keep the field free of weeds and remove any unwanted buds promptly. One month after emergence, apply 100 kg of bean cake or 150–225 kg of ammonium sulfate per 667 m². Water regularly but avoid overwatering. Maintain a "yellow grass" condition, which means keeping the soil slightly dry. Use the "three pouring and three pouring" method: water after fertilizing, use cool water after thunderstorms, and water during midday if plants show signs of wilting. Avoid watering during extreme heat or heavy rain.
4. **Pest and Disease Control**:
- **Yellow Leaf Spot Disease**: Affects leaves, especially during July and August. Control by selecting disease-free areas, removing infected plant material before harvesting, and applying fungicides like chlorothalonil or Bordeaux mixture.
- **Yellow Wilt Disease**: Caused by soil-borne pathogens. Prevention includes crop rotation, using disease-free seeds, and improving drainage.
- **Soybean Cyst Nematode**: Damages roots. Prevent by avoiding continuous cropping and using warm water soaking or soil disinfection.
- **Cotton Red Spider**: Feeds on leaves. Control by removing diseased plants, keeping a distance from cotton fields, and spraying insecticides like amifenturon or amitraz.
**Harvesting and Processing**: Rehmannia is harvested in September or October. Dig up the roots, clean off excess soil, and then process them. Fresh roots are slowly dried over a fire until they become black and soft. Once hardened, the outer skin is removed. After 1–2 days of rest, the roots are fully dried. For processed Rehmannia, soak the raw roots in 50% rice wine, seal them in containers, and steam them in a water bath until the wine is absorbed. Finally, sun-dry until the surface is slightly dry.
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