Detailed Explanation of the Key Cultivation and Management Techniques for Rehmannia

Rehmannia from Wen County, Wuzhi, and Mengzhou yields the largest harvest and the best quality, and is known as Huai Rehmannia.

Growth Habits

Rehmannia grows wild on hillsides, roadsides, and field edges. It prefers a mild climate and needs ample sunlight; its tuberous roots grow rapidly when the temperature is 25°C to 28°C. It is not demanding about soil and can even be planted in fertile clay. It is cold-tolerant, drought-tolerant, and fertilizer-loving, but fears waterlogging and should not be grown in continuous cropping. Its growth and development are divided into four stages: the seedling stage (from planting and emergence until the plant diameter reaches 10 cm, April to June), the rosette stage (rapid leaf growth, June to July), the tuberous root enlargement stage (slow leaf growth and rapid tuberous root enlargement, July to September), and the mature harvest stage (aboveground growth stops, October). Rehmannia overwintering in the same year buds and flowers in April of the following year, and its fruits mature in June.

Cultivation Techniques

1. Site selection and land preparation. Choose an open, sunny plot with a low groundwater table, preferably loose, fertile, well-drained sandy loam. The previous crop should preferably be a grass-family crop such as wheat or corn. After the previous crop is harvested in autumn, plow deeply to about 30 cm. In the following spring, apply 4000 to 5000 kg of barnyard manure, 50 kg of superphosphate, and 50 to 100 kg of cake fertilizer per mu, spreading them evenly over the ground (preferably by opening furrows and applying in bands), then shallow-plow once more, rake fine, and level. Make flat beds or raised beds 1.2 m wide, or form 60 cm high ridges.

2. Propagation Methods. Because Rehmannia tuberous roots have many buds and readily root and sprout, tuberous root propagation is mostly used, though seed propagation can also be used (mostly for breeding).

1. Tuberous root propagation.After the spring Rehmannia is harvested in autumn, select disease- and pest-free tuberous roots of good shape and 1 to 2 cm thick, and store them in a cellar in sand for seed. Alternatively, select well-grown plants and leave some undug in the field to overwinter in the open, then dig them up in the following spring as seed. Because climate conditions and varieties differ from place to place, planting time also differs, but generally it can be divided into early Rehmannia and late Rehmannia; early Rehmannia is planted in early to mid-April, and late Rehmannia from late May to early June. When planting, on the prepared bed surface, open furrows at a row spacing of 30 cm, place the rhizomes at a plant spacing of 15 to 20 cm, and cover with 3 to 4 cm of soil. About 40 kg of tuberous roots are needed per mu.

2. Seed propagation.The seedling transplanting method is mostly used, sowing and raising seedlings in late March. Open shallow furrows at a row spacing of 10 to 15 cm and sow in rows, covering with 0.3 to 0.5 cm of soil. Spray water frequently to keep moist. Seedlings emerge 15 days after sowing. When the seedlings have grown 6 to 8 leaves, they can be transplanted to the field. Transplant at a row spacing of 20 cm and a plant spacing of 15 cm, harvest in autumn; the large ones can be used as medicine, and the small, robust, and plump ones are selected as seed. After continuous selective propagation of Rehmannia tuberous roots, the yield and quality are better than those from many years of asexual propagation; to prevent degeneration, these two propagation methods should be used alternately.

Field Management Rehmannia has shallow roots, so hoe shallowly to avoid damaging the roots. Generally, hoe shallowly 3 times before the rows close, with the last hoeing slightly deeper. Combined with intertillage, apply 2000 kg of human and animal manure and 50 kg of cake fertilizer per mu for the first topdressing, and for the second topdressing apply 2500 kg of human and animal manure, 50 kg of cake fertilizer, and 50 kg of superphosphate per mu (if base fertilizer has already been applied, superphosphate and cake fertilizer should not be applied or should be applied sparingly). Before the rows close, a third topdressing can also be carried out with a slight increase in phosphate fertilizer based on the amount of the second topdressing. Water little and often; do not flood-irrigate. In the rainy season, drain field water promptly to prevent root rot. Except for plants kept for seed, remove flower stalks promptly. Rehmannia can grow slender roots along the ground surface from the tuberous roots, called surface-running roots, and these should all be removed.