Key Cultivation Techniques and Field Management Methods for Rhubarb
Rhubarb, also known as Shengjun, Jiangjun, and Chuanjun. Its nature and flavor are bitter and cold. It has the effects of purging excess heat, removing accumulated stagnation, resolving blood stasis, and detoxifying. It is used for excess-heat constipation, abdominal pain from accumulation and stagnation, damp-heat jaundice, acute appendicitis, incomplete intestinal obstruction, and other conditions. It is mainly produced in Qinghai, Gansu, Sichuan, Shaanxi, and other provinces.
Morphological Characteristics
Rhubarb is a perennial herbaceous plant in the Polygonaceae family. Its root is fleshy and enlarged, lignified, unbranched, and radish-shaped; some have several branches and are ox-head-shaped. The stem is upright, unbranched, 90-120 cm tall, hollow, with longitudinal grooves and short pubescence. The basal leaves are large, nearly round, and palmately parted. The inflorescence is paniculate, with dense branches; the branchlets are upright and several are clustered at each node. The flowers are small, several clustered together, greenish-white or deep purple. The achene is red, triangular, oblong, with 3 winged angles, rounded or slightly concave at the top, and cordate at the base.
I. Growth Habits
It prefers a cool climate, is cold-tolerant, and dislikes high temperatures. It grows wild in the high mountain areas of northwest and southwest China at about 2000 m above sea level; cultivated plants are grown in areas above 1400 m. Climatic conditions: the minimum winter temperature should be above -10°C, the summer temperature should not exceed 30°C, the frost-free period is 50-180 days, and annual rainfall is 55-1000 mm. It has strict soil requirements; generally, loam or sandy loam with deep soil layers, rich in humus, and well drained is best. Planting in heavy acidic soil causes poor rhizome growth and affects yield. Plots with poor drainage or an excessively high groundwater table are not suitable for planting. Rhubarb should not be continuously cropped; it must be replanted only after 4-5 years, and it is best rotated with leguminous or grass-family crops, or preceded by Codonopsis pilosula or Coptis chinensis.
Rhubarb seeds germinate easily. At 15-25°C, the germination rate can reach over 85%, and seed viability is 1-2 years.
II. Site Selection and Land Preparation
Rhubarb is a deep-rooted plant, and the main root can penetrate 30-45 cm into the soil. A loose, well-drained sandy loam hillside is best for site selection. After harvesting the previous crops such as corn and potatoes, apply sufficient base fertilizer together with deep plowing, applying 4000-5000 kg of barnyard manure per mu; on poor soil, the amount of fertilizer can be increased.
III. Sowing
Rhubarb is mainly propagated by seed, and can also be propagated by buds. Seed propagation is further divided into direct sowing and seedling transplanting.
1. Direct sowing: carried out in early autumn or early spring. For direct sowing, use hole sowing at a row spacing of 70 cm x 60 cm, with holes about 3 cm deep, sowing 5-6 seeds per hole, and covering with about 2 cm of soil. The seeding rate is 2-2.5 kg per mu.
2. Seedling raising and transplanting: to save seeds and improve land utilization, or in areas with spring drought where direct sowing is unsuitable, sowing and seedling raising followed by transplanting to the field is often used. The method is to prepare the land into raised beds 1.2 m wide and 21 m long, with drainage ditches opened on all four sides. Open furrows across the bed for drilling, with a row spacing of 12 cm and a depth of 5 cm, sow the seeds evenly into the furrows, cover with 2-3 cm of soil, and then cover with a layer of straw. After germination and emergence, remove the straw covering. Pay attention to weeding, and in May-June apply some dilute human urine and feces as a topdressing. In late October during overwintering, earth up 3-5 cm along the rhubarb seedling rows to prevent damage to the seedlings, and transplant in the second year.
In the second year of seedling raising, transplant in mid-April (Grain Rain) or late August (End of Heat). After digging out the seedlings, trim off the lateral roots, and plant them promptly in the prepared land, with a spacing of 60 cm between plants and rows, digging holes 15-30 cm deep, 1 plant per hole, covering with soil, burying the crown, and firming the soil so that the roots and soil are closely combined.
When transplanting, "curved-root planting" can be adopted, that is, when planting, bend the tip of the seedling root upward into an L shape, which can greatly reduce the bolting rate of the plant.
3. Bud propagation: when harvesting rhubarb, remove the robust and relatively large buds sprouting from the rhizome of the mother plant and plant them. Smaller buds can be planted in a seedling bed and transplanted in the autumn of the second year. To prevent rotting at the wound, apply plant ash to the wound when planting.
IV. Field Management
1. Intertillage and weeding: in the first year, rhubarb seedlings are small and weeds easily grow, so weed frequently while loosening the soil; plant soybeans and corn between the rows to suppress weed growth. In the second to third years, weed and loosen the soil in early May and mid-July, and earth up more around the roots.
2. Fertilization: rhubarb is a fertilizer-loving plant. In addition to base fertilizer, topdressing is needed 2-3 times each year. In June of the first year, apply 50 kg of cake fertilizer and 10-20 kg of superphosphate per mu. In the second year, apply topdressing twice, in May and June respectively, by opening furrows between the rows and applying human urine and feces, or 20-30 kg of superphosphate and 10-20 kg of potassium chloride, then covering with soil and watering.
3. Bolting removal: after rhubarb is planted, it begins to bolt and flower in the second year. Except for land kept for seed production, the flower stalks of the remaining plants should be removed, and bolting removal should be done on sunny days.
V. Pest and Disease Control
The main disease is root rot, which mostly occurs during the rainy season in August-September, or under high temperature and high humidity, often in the same year as rhubarb harvest or in the previous year. The top of the root begins to turn black and rot, and the leaves simultaneously turn yellow and even die. Control methods are to pay attention to draining accumulated water and loosen the soil in time. After bolting removal, cover the wound from bolting removal well with soil, or disinfect with quicklime water. After disease onset, pull out diseased plants as early as possible, and in autumn collect dead branches and leaves and burn them to reduce sources of the pathogen.
Pests include aphids, which cause serious damage in June-July and can be sprayed with 2000-fold dimethoate emulsion. Rodent damage can be controlled by trapping or manual killing.
VI. Harvesting and Processing
After rhubarb has been planted for 2-3 years, harvest in September-October when the aboveground parts wither. When harvesting, first cut off the aboveground parts, dig out all the rhizomes and roots, carefully shake off the soil, cut overly large rhizomes into several pieces, and cut medium and small ones into slices, then air-dry, sun-dry, or oven-dry them. After drying, place them in wooden boxes or impact medicine-processing equipment and strike them to remove the rough bark until the yellow color is exposed. About 400 kg of dried goods can be harvested per mu.
VII. Seed Production Techniques
Select robust three-year-old plants free of pests and diseases and relatively pure in variety, strengthen field management, and set up supports in May when flower stems bolt to prevent them from being broken by wind. Seeds are very easily blown off by wind when mature, so growth conditions should be checked frequently. In mid-to-late July, when some seeds turn dark brown, cut them back promptly, place them in a ventilated and shaded place for after-ripening, and after several days shake them off for use as seed. Seeds for spring sowing should be dried in the shade and stored, and must not be allowed to become damp and moldy.