Detailed Explanation of Key Techniques for Understory Cultivation and Management of Asarum

Asarum is a perennial herbaceous medicinal plant of the genus Asarum in the family Aristolochiaceae, with antipyretic, wind-dispelling, diaphoretic, expectorant, and analgesic effects. Wild asarum is mainly distributed in the forest regions of Liaoning and Jilin.

Asarum is a shade-loving plant, but if the understory temperature is too low and the light too weak in its wild state, it grows extremely slowly. Generally, understory cultivation takes more than 6 years from planting to harvest, and the plants are short, with only 2-3 leaves per plant, yielding very little. Farmers are accustomed to digging up wild asarum in May, when the seeds are not yet ripe, which seriously affects the natural reproduction of understory asarum. Due to forest logging and changes in the natural environment, the resource has been severely damaged, and over-digging in particular has brought wild asarum to the brink of extinction.

1. Site Selection and Land Preparation

Wild asarum is a shade-loving plant that grows under the forest. Because it has long grown in the moist, fertile humus layer under the forest, it has developed characteristics of preferring moisture, preferring fertilizer, preferring shade, and fearing strong light. It is commonly found among dense shrubs, in slightly moist spots at the bottom of mountain gullies, and at forest edges and shaded rocky wet areas. Therefore, for understory cultivation, a forest area with complete vegetation and fertile soil should be selected. First, thin out overly dense and unmarketable trees or remove overly dense branches. Generally, plow the soil to 15 cm, then rake out residual roots and weeds, and make beds following the slope for later use.

2. Seed Propagation and Seedling Transplanting

For artificially cultivated asarum, direct seeding can be harvested in one go after 5 years; for seedlings transplanted after raising, they are harvested after 3-4 years of growth following transplanting.

2.1 Sowing and Raising Seedlings

In mid-to-late June, when the fruit turns from purplish red to pinkish white, and the flesh feels soft when pinched and appears powdery and sandy, it is ripe. It should be harvested as it ripens, otherwise the seeds easily fall off and are carried away by ants. After harvesting the seeds, rub off the fruit skin and sow immediately. The seeds must be fresh; dry seeds stored indoors for 2 months will lose their germination ability. If the seeds cannot be sown in time after collection, the newly harvested and washed seeds should be mixed with wet sand and buried for storage until sowing. The sowing period must not be later than the end of July; if too late, it affects root growth.

Sowing methods include broadcast sowing, drill sowing, and hole sowing. ① For broadcast sowing on a high bed, level the bed surface, make a bed trench 5 cm deep, rake the bottom of the trench flat, and then sow. Fresh seeds can be mixed evenly with 5-10 times their volume of fine sand and then broadcast. The sowing rate is 20 g per square meter; sowing must be uniform, and after sowing cover with 1.5 cm of soil. ② For drill sowing, open furrows on the bed surface at a row spacing of 10-15 cm, with a furrow depth of 1.5 cm. Mix the seeds with fine sand and evenly scatter them into the furrows, then cover with 1.5 cm of soil. The seeding rate is 4-5 kg per mu. ③ For hole sowing, press the bed surface with a wooden roller, sow at 10 x 10 cm, with 5-7 seeds per hole, and cover with 2 cm of soil. The seeding rate is about 2.5 kg per mu. Then cover the bed surface with a layer of half-rotted tree leaves. With the above propagation methods, after emergence the plants grow for 4-5 years and can be harvested in one go for sale as a commodity. If raised as seedlings for transplanting, small seedlings that have grown for 2-3 years can be transplanted.

2.2 Transplanting

2.2.1 Transplanting of wild asarum seedlings is carried out in May-June. At this time asarum has grown larger while other weeds have not yet grown up, making it easy to find and dig up. When digging seedlings, do not damage the roots and bud scales; after digging, keep them fresh and prevent them from drying out, and transplant immediately after collecting. The transplanting row spacing is 15 cm and the hole spacing is 20 cm. Be careful to straighten out the fibrous roots.

2.2.2 Seedling transplanting is best done in spring before the bud scales begin to sprout and in autumn after the aboveground plants have withered. If transplanting in summer, watering is needed. When transplanting, open furrows across the bed surface, with a row spacing of 20 cm and a plant spacing of 6 cm. If the soil tends to harden, hole planting is preferable, with plant and row spacings of 25 x 25 cm or 20 x 20 cm respectively, 3-5 plants per hole, and cover with 4 cm of soil after planting.

3. Field Management

3.1 Fertilization and Earthing Up

The most important experience summarized from asarum production is that applying more manure promotes rapid growth and high yield. Applying rotted pigpen manure and sheep, rabbit, and chicken manure is best, and combining it with chemical fertilizers containing phosphorus and potassium gives even better results. Each spring, before the asarum bud scales begin to sprout, along with loosening the soil, apply 50 kg of superphosphate per mu, or apply 10-20 kg of compound fertilizer (or diammonium phosphate). In autumn, spread fully rotted pig manure or sheep manure onto the bed surface as a top-covering fertilizer; apply 1.5 cm for 1-year-old seedlings and 3 cm thick for 2-3-year-old seedlings. The top-covering manure can serve to topdress, protect against cold, retain moisture, and prevent freezing damage. In addition, in spring, summer, and autumn each year, use soil from the work paths to build up the bed edges, to prevent rainwater from washing away the bed edges and exposing the overwintering buds, rhizomes, and fibrous roots.

After artificial cultivation, through fertilization and increased light, asarum leaves can become thicker, photosynthesis can be strengthened, and growth can be promoted; asarum has well-developed rhizomes with many branches, thick and long fibrous roots, enlarged terminal buds on the rhizome nodes, and both lateral buds and dormant buds form relatively large overwintering buds, so that the number of leaves doubles the next year. Each hole originally planted with 3-4 plants has 6-12 leaves, and after 5 years of growth the leaves can reach 80-200. There is a great difference between fertilized and unfertilized asarum.

3.2 Weeding and Loosening the Soil

Throughout the entire growth process of asarum, weeding and loosening the soil should be carried out 3-5 times each year to keep the bed surface free of weeds.

3.3 Bed Surface Mulch Management

In early April, remove the mulch on the bed surface from sowing to facilitate emergence. In mid-to-late April, when the seedlings have basically all emerged, scatter larch needles onto the bed surface to prevent rainwater from washing away the bed surface and soil compaction, to prevent drought, and to reduce weeds.

3.4 Adjusting Light

After the soil freezes, the tree canopy should be trimmed according to the different ages of the asarum to adjust light. Because asarum grows in a deep humus soil layer, its root system is not well developed and only forms a shallow root system, so it cannot absorb deep water and therefore is not tolerant of drought. Asarum fears strong sunlight and must have shading conditions to survive. A few hours of direct exposure to the scorching sun in June will cause all asarum plants to wither and die; but sufficient oblique dappled light will promote rapid growth; if the forest canopy density exceeds 70%, growth is extremely slow. In artificially cultivated asarum, through fertilization, watering, and providing sufficient oblique dappled light, growth is faster and yield is higher.

3.5 Adding Cold Protection Cover in Autumn and Winter

Before the soil freezes in autumn, it is necessary to cover with fallen leaves or weeds without grass seeds, in order to keep warm, retain moisture, prevent freezing damage, avoid the drying up of asarum buds and rhizomes, and prevent frost heaving.