Planting Methods and Key Technical Points for the Chinese Medicinal Herb Rehmannia

Rehmannia is a perennial herbaceous plant of the genus Rehmannia in the family Scrophulariaceae (figwort family), reaching a height of up to 30 cm, with a fleshy rhizome that is yellow when fresh and purplish-red stems under cultivation conditions. The diameter can reach 5.5 cm, the leaves are ovate to oblong-elliptic with sunken veins on the upper surface, the flowers are arranged in a somewhat raceme-like inflorescence at the top of the stem, the corolla is purplish-red outside and yellow-purple inside, the anther cells are oblong, and the capsule is ovate to oblong-ovate; the flowering and fruiting period is April to July.

Growth Habits of Rehmannia

Wild rehmannia grows on hillsides, roadsides and field edges. It prefers a mild climate and requires ample sunlight; the tuberous roots grow rapidly when the temperature is 25°C-28°C. It is not demanding about soil and can also be planted in fertile clay. It is cold-tolerant, drought-tolerant, fertilizer-loving, afraid of waterlogging, and intolerant of continuous cropping.

Seed Selection and Planting of Rehmannia

Generally, cultivated rehmannia uses the rhizome as propagation material, which is called a "seed piece" in production. For rehmannia "seed pieces", the "inverted planting" "seed pieces" cultivated in July-August of the previous year are generally selected, because when "inverted planting" "seed pieces" are used as seed, rehmannia has high yield, good quality, and can prevent variety degeneration. Before planting, remove the head and tail of the "seed piece" and take the middle section. Then cut it into small sections 3-6 cm long, each section retaining two to three buds, dip the cut ends in plant ash, let them dry slightly, and then plant. The general planting density is 30-40 cm between rows and 25-30 cm between plants. On the prepared ridge surface, dig small holes 3-5 cm deep, place 1-2 sections of "seed piece" horizontally in each hole, cover with 1 handful of burned soil ash mixed with manure water, and then cover with fine soil level with the ridge. Each mu requires 40-60 kg of "seed pieces". Note that when selecting seed, try to use "inverted planting" "seed pieces" and avoid using small commercial ones; at the same time, the "old mother tubers" should be removed from the "seed pieces". That is, the seed pieces planted in the first ten days of the month.

Field Management of Rehmannia

1. Timely thinning and replanting. When the seedlings are 10-12 cm tall, begin thinning, leaving 1 strong seedling per hole. If there are missing plants, replant promptly on cloudy days, and when replanting, lift the seedlings with soil so that the survival rate is higher;

2. Intertillage and weeding. The rhizome of rehmannia goes into the soil relatively shallowly, so intertillage should be shallow to avoid damaging the roots. Weeds around the seedlings should be pulled out by hand. After the plants close their rows, stop intertillage;

3. Topdressing. Rehmannia likes fertilizer. In addition to applying sufficient base fertilizer, after thinning apply 100 kg of superphosphate and 30 kg of decomposed cake fertilizer per mu to promote rhizome development and expansion. When the rows close, broadcast 1 application of burned soil ash between the rows to promote robust plant growth;

4. Irrigation. Rehmannia needs a large amount of water in the early stage, so it should be watered frequently. In the later stage, which is the period of underground rhizome expansion, water should be used sparingly. During the rainy season, drainage should be done promptly to prevent root rot;

5. Remove creeping surface roots. In addition to the main root, rehmannia can also grow slender underground stems along the soil surface, called creeping surface roots. These creeping surface roots consume a relatively large amount of nutrients and should be removed promptly.

Pest and Disease Control of Rehmannia

The main diseases of rehmannia are leaf spot disease, ring spot disease and fusarium wilt. These diseases generally begin to occur in early May and are severe in June-July, so timely control should be noted. Pests include red spiders, cutworms, white grubs, and others. These are controlled by conventional methods, and when choosing pesticides, avoid using highly toxic pesticides.

Harvesting and Processing of Rehmannia

For spring-planted rehmannia, when the aboveground stems and leaves wither and turn yellow around November of the same year, they should be dug up promptly. When digging, open a 35 cm deep trench at one end of the ridge and carefully remove the rhizomes one by one. For processing rehmannia, use a special roasting oven to process it into prepared rehmannia, which then becomes a commercial product.