Detailed Explanation of Key Techniques for Understory Cultivation of Asarum heterotropoides var. mandshuricum

Asarum heterotropoides var. mandshuricum (northern wild ginger, Liaoning wild ginger), a perennial herb of the genus Asarum in the Aristolochiaceae family, is used medicinally as a dried whole plant. It has the effects of dispelling wind and dispersing cold, opening the orifices and relieving pain, and warming the lungs and resolving phlegm. It is mostly distributed in the eastern mountainous areas of the three northeastern provinces.

1. Biological characteristics

1.1 Growth and development

Asarum heterotropoides var. mandshuricum is a perennial herbaceous plant. It usually takes 5-7 years from sowing to the formation of new seeds, after which it flowers and sets seed every year. Within a year, the flowers and leaves of wild ginger open in early spring; by May the aboveground plants have basically finished growing, stop growing, and do not put out new leaves; in July the buds differentiate, and by autumn they form complete overwintering buds, then grow and develop again the following year.

1.2 Biological characteristics of the seeds

1.2.1 Short seed lifespan. Naturally matured seeds have a germination rate of over 95%; after being stored under dry conditions at room temperature for 20 days, the germination rate is about 80%; after 40 days, about 29%; after 60 days, 2%. This shows that the germination rate of dry-stored seeds gradually decreases as the storage period lengthens, and once the storage period exceeds 60 days, they completely lose viability. Therefore, seeds should be sown immediately after collection; if for some reason they cannot be sown in time, store them buried in moist sand (1 part seeds mixed with 3-5 parts river sand). After storage in moist sand for 1-2 months, the germination rate is still above 80%; this method can also be used to transport seeds over long distances.

1.2.2 Relationship between growth and development and environmental conditions. (1) Temperature: Under conditions of 20-24°C with suitable humidity, seeds complete morphological after-ripening in about 50 days and germinate and root at 17-21°C; after rooting, seeds kept at 0-5°C for 50 days will germinate when given suitable conditions. Seedlings emerge when the field surface temperature is 10-12°C, flowering begins at 17°C, and during dormancy they can withstand severe cold of -40°C. (2) Water and fertilizer: Asarum heterotropoides var. mandshuricum is a fibrous-rooted medicinal plant. During seed germination, a soil moisture content of 30-40% is suitable; during the growing period it is afraid of waterlogging, and young seedlings are afraid of drought. Drought before and after emergence not only lowers the emergence rate but also lowers the seedling survival rate. (3) Light: Asarum heterotropoides var. mandshuricum is a shade-loving medicinal plant. From direct seeding to emergence, light is needed. At 1-2 years of seedling age, shading is needed, and the canopy density for understory cultivation should be controlled at 0.6-0.7. For 3-4-year-old seedlings, the canopy density should be controlled at 0.3-0.4.

2. Cultivation techniques

2.1 Site selection and land preparation

Wild ginger prefers a cool, moist environment and loam or sandy loam rich in humus and well drained. The soil layer of the plot should be deep, and the soil should be loose, fertile, and moist. The slope of woodland should be below 15°. When raising seedlings under forest, choose flat broad-leaved woodland with sparse trees. In conjunction with forest tending, cut down the trees on the beds that can be felled, appropriately widen the distance between beds, retain all trees between beds, and where they are too dense, appropriately thin the tree canopy. Beds should run diagonally across the slope, avoiding a due north-south orientation as much as possible. After selecting the site, plow to a depth of about 20 cm, break up the soil, remove tree roots, weeds, stones, and other debris, and then make the beds. Generally the beds are 1.2 m wide and 15-20 cm high; the bed surface should be level, and the distance between beds is 50-80 cm.

2.2 Sowing and transplanting

2.2.1 Direct seed sowing

2.2.1.1 Seed collection: The fruits mature in mid-to-late June and should be collected as they ripen. Generally, fruits ripen faster on rainy days, so they should be harvested promptly. After picking, the fruits should be placed in a cool place for 2-3 days; once the fruit skin becomes soft and powdery, rub off the skin and flesh, wash the seeds out with water, drain the water or dry them in a cool place, and then sow them fresh.

2.2.2.2 Sowing: Generally from early to mid-July, and no later than early August. The sowing methods are broadcast sowing and drilling in rows. (1) Broadcast sowing: Dig shallow furrows 3-5 cm deep on the bed surface, level the bottom of the furrows with sifted fine humus soil, and then sow. When sowing, mix the seeds with 5-10 times their volume of fine sand or humus soil and scatter evenly. After sowing, cover with 0.5-1.0 cm of sifted fine humus soil. After covering with soil, spread a layer of fallen leaves over the bed surface. The amount of fresh seed used for sowing is about 120-140 g/sq m. (2) Drilling in rows: Open shallow furrows 3-5 cm deep across the bed surface, with a row spacing of 10 cm and a furrow width of 5-6 cm; level the furrow bottom and press it lightly, then sow in the wide furrows, cover with 0.5-1 cm of soil, and finally cover with fallen leaves. The amount of fresh seed used for sowing is about 100 g/sq m. (3) Seedbed management: After sowing, in the spring of the following year, when the bed soil thaws, remove the covering; if drought occurs, water promptly. Although wild ginger is a shade-loving plant, it still needs a certain amount of light during growth and development. Generally, 1-2-year-old plants have weak light resistance, so shading can be somewhat greater, with a canopy density of 0.6-0.7 being suitable; 3-4-year-old plants have strong light resistance, so a canopy density of 0.4 is suitable.

2.2.2 Seedling raising and transplanting

Every year in October, dig up 2-3-year-old seedlings and plant them separately in three grades: large, medium, and small. When planting, open furrows across the bed with a row spacing of 15 cm and a furrow depth of 9-10 cm, and a plant spacing of 8-10 cm, so that the fibrous roots spread out well, then cover with 3-5 cm of soil. For spring transplanting, it should be done before the buds sprout. Seedbed management is the same as for direct seed sowing.

2.3 Pest and disease control

2.3.1 Diseases Sclerotinia rot is the main disease of wild ginger. It spreads quickly and causes severe damage. Sources of infection: mainly seeds, seedlings, and infested soil carrying the pathogen. In the field, diseased plants generally appear first, then spread and expand, forming disease spots, disease beds, and disease areas. The main route of transmission is human activity. In addition, pests and rodents also play a certain role in transmission. Air cannot transmit it. Therefore, under natural conditions the disease spreads relatively slowly, while human transmission is faster. Once a diseased field forms, the entire plow layer is occupied by the pathogen, forming a permanent diseased field that is very difficult to control. Control measures: (1) Investigation of producing areas: Strictly blockade any diseased areas found, prohibit the transport of diseased seeds and seedlings out of the area, and prevent human transmission. Diseased areas and beds must be thoroughly treated. (2) Establish bases for disease-free seeds and seedlings. (3) Disinfection of seeds, seedlings, and tools: Use a mixture of 800 times diluted amobam and 200 times diluted 10% carbendazim to soak seeds and seedlings separately for 3-4 h. When disinfecting for sowing and transplanting, do not use injured seeds or seedlings to prevent phytotoxicity. (4) Chemical control: For diseased areas and diseased plants, use the above medicinal solution, open furrows, and pour it around the diseased plants and the nearby healthy plants, and spray the aboveground parts of the plants. From early April to the end of May and from early September to the end of October, carry out about 5 treatments in total.

2.3.2 Insect pests (1) Black cutworm: bites buds and cuts off leaf stalks and rhizomes. Control: use poisoned soil and poisoned bait to trap and kill. (2) Larvae of the wild ginger swallowtail - black hairy caterpillars: mainly bite leaves. Control: spray 0.1% wettable trichlorfon on the leaf surface.

3. Harvesting and processing

3.1 Harvesting

Direct-seeded Asarum heterotropoides var. mandshuricum is generally harvested for medicinal use after 3-5 years; for transplanted seedling plots, it is harvested for medicinal use after 3-4 years. Harvesting is generally done in August.

3.2 Processing

After harvesting wild ginger, remove all soil, tie into bundles of 10 plants each, and dry in a cool, ventilated place in the shade. It must not be washed with water or exposed to the sun. After washing with water and drying, the leaves turn black and the roots turn white. After sun exposure, the leaves turn yellow, reducing the aroma and affecting quality.