Detailed Explanation of Key Techniques for Artificial Cultivation of Rehmannia

Rehmannia, also known as Jiuhu Hua, is a plant of the Scrophulariaceae family, with its roots used as medicine. Fresh rehmannia has the effects of clearing heat, promoting fluid production, and cooling blood; dried rehmannia has the effects of clearing heat, promoting fluid production, moistening dryness, cooling blood, and stopping bleeding; prepared rehmannia has the effects of nourishing yin and tonifying the kidneys, regulating menstruation, and enriching blood. Rehmannia is mainly produced in Hebei, Inner Mongolia, Liaoning, and other places. Rehmannia prefers a mild climate environment with ample sunlight; when the temperature is below 8°C, the rhizome is prone to rot. Continuous cropping is avoided, and cotton, peanuts, sesame, legumes, and similar crops should be avoided as previous crops. The cultivation plot should be selected with loose soil and good drainage for planting; deep plow about 30 cm, rake level and fine, make flat beds 120 cm wide, and apply sufficient base fertilizer during land preparation.

1. Propagation and cultivation: When rehmannia is harvested in the same year, select high-quality rhizomes, store them in a cellar, and plant them in the field in the spring of the following year when the temperature steadily exceeds 12°C. Before planting, cut the rehmannia into 3—5 cm long sections, each retaining more than 3 plump buds, then open furrows about 30 cm apart and about 6 cm deep, and plant the rhizomes into the furrows at a plant spacing of 15—20 cm. After planting, cover with 6—8 cm of soil, press lightly, and water. Usually, seedlings emerge about 25—30 days after planting. If sprouting is promoted before planting, seedlings emerge quickly and uniformly. After emergence, attention should be paid to preventing frost in spring.

2. Field management: From emergence until the rows close, weed and loosen the soil frequently, remove flower buds and tillers at any time, and apply topdressing 1—2 times, water timely to prevent drought, and pay attention to timely drainage during the rainy season to strictly prevent waterlogging in the field.

3. Disease control: First, spot blight, with round or irregular yellow or brown lesions on the leaf surface. At the early stage of the disease, spray 1:150 Bordeaux mixture once every 10—15 days, for 3—4 consecutive sprays. Or use zineb 500—600 times solution, spraying once every 7—10 days, for 3—4 consecutive sprays. Second, ring spot, with yellow-brown lesions on the leaf surface, showing obvious concentric rings, with small black dots on them; the control methods and agents can be the same as for spot blight.

4. Harvesting: Usually harvested in October after growth stops. First cut off the aboveground part, dig out the rhizomes, and remove the soil to obtain fresh rehmannia. The usual yield is 1500—3000 kg of fresh rehmannia per mu.

5. Processing: Dry the rhizomes of rehmannia; before drying, remove the soil and grade them by size for baking. During baking, turn them while baking. When the rhizomes are baked until they have no hard core and are soft in texture, take them out and pile them for sweating. After “sweating,” bake until the rhizomes reach “sugar maturity,” then take them out, place them in a cool place for 2 days, and sun-dry them to obtain dried rehmannia.