Detailed Explanation of High-Yield Cultivation Techniques and Production Measures for Rehmannia (Chinese Foxglove)

I. Site Selection and Land Preparation.

Choose sandy loam soil with deep, fertile soil and good drainage. In the winter of the previous year or early spring, plow the soil deeper than 25 cm, and at the same time apply 2000-3000 kg of decomposed compost and 25 kg of superphosphate per mu as base fertilizer. Then, level and rake the soil fine to make beds, generally 1.3 m wide. Pay special attention that Rehmannia should not be planted in continuous cropping, which is also a key measure to note in site selection.

II. Seed Selection and Planting.

Generally, Rehmannia is cultivated using rhizomes as propagation material, called "planting stock" in production. For Rehmannia "planting stock," generally the "reverse-planted" "planting stock" cultivated in July-August of the previous year is selected, because when "reverse-planted" "planting stock" is used as seed material, Rehmannia yields are high, quality is good, and variety degeneration can be prevented. Before planting, remove the head and tail of the "planting stock" and take the middle section. Then cut it into small sections 3-6 cm long, each section retaining two to three bud eyes. Dip the cut ends in plant ash, let them dry slightly, and then plant. Generally, the planting density is 30-40 cm between rows and 25-30 cm between plants. Dig small holes 3-5 cm deep on the prepared bed surface, place 1-2 sections of "planting stock" horizontally in each hole, cover with a handful of burnt soil ash mixed with manure water, and then cover with fine soil level with the bed. Each mu requires 40-60 kg of "planting stock." Note that when selecting seeds, try to use "reverse-planted" "planting stock," avoid using small commercial stock, and the "planting stock" should have the "old mother root" removed. That is, the seed stock planted in the previous ten days.

III. Field Management.

1. Timely thinning and replanting. When 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 seedlings with soil, which gives a higher survival rate;

2. Cultivation and weeding. Rehmannia rhizomes are relatively shallow in the soil, so cultivation should be shallow to avoid damaging the roots. Weeds around the seedlings should be pulled by hand. After the plants close the rows, stop cultivation;

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 burnt soil ash once 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 underground rhizome expansion period, 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 relatively more nutrients and should be removed promptly.

IV. Pay Attention to Preventing Diseases and Pests.

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 become severe in June-July, so timely prevention and control should be noted. Pests include red spiders, cutworms, and white grubs, etc. These are controlled by conventional methods, and when choosing pesticides, avoid using highly toxic pesticides.

V. Harvesting and Processing。

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