Cultivation Techniques and Field Management Methods for Sweet Wormwood

Sweet WormwoodPlant height 40—150 cm, the whole plant has a strong volatile oil odor. Stem erect, with longitudinal stripes, much branched, smooth and hairless. Basal leaves lie flat on the ground, withering at flowering; cauline leaves alternate, green when young, turning yellow-brown when old, hairless, with short petioles, gradually becoming sessile upward; leaf blades usually once pinnately parted, lobes short and fine, with very small powdery short pubescence, dark green above, light green below, with fine hairs or powdery glandular dots; the leaf rachis has narrow wings on both sides; the leaves on the upper part of the stem gradually become smaller upward and linear. In late autumn it bears small yellow flowers, capitula small, spherical, about 3.6 mm in diameter. With fine soft short pedicels, mostly forming panicles; involucre small spherical, all flowers tubular, yellow, the outer ones female flowers, the central ones bisexual flowers, achenes, elliptic. Flowering period in July—August, fruiting period in September—October.

There are also plants of the same genus, Artemisia annua and its variety Artemisia annua var. macrocephala. The differences between the two and sweet wormwood are: the leaves are three times pinnately parted, the central axis is not pectinate, the final small lobes are short and pointed, easily broken, and the pith of the cross-section is relatively large. The capitula are spherical and relatively dense, 1.5 mm in diameter for Artemisia annua; the capitula are spherical and relatively dense, 3 mm in diameter for Artemisia annua var. macrocephala.

[Growth Habits]

1. Biological Characteristics

(1) The thousand-seed weight of seeds is 0.02—0.048 mg, with 4500—5000 seeds per gram. Seed germination requires light or alternating temperature. Under light, at 15℃—25℃, germination occurs, with a seed germination rate of 99%; below 15℃ or above 30℃ the seed germination rate is relatively low.

(2) Growth period: sown in early March (10.5℃), emergence in 7 days, the first pair of true leaves grows out in 12 days. After emergence, growth accelerates at 40 days, seedling height 18 cm; at 80 days it bolts, and at 39 cm the first branching occurs; in mid-to-late June it enters the second branching. From the first branching to budding requires 130 days, after 170 days (early August to late September) it flowers, after 200 days (late September to early October) the fruit ripens (15.7℃), after 260 days (late December) the plants lodge (5℃—8℃). From sowing to leaf harvest is 172 days, and the whole growth cycle is 265 days.

(3) Root growth: sweet wormwood is a shallow-rooted plant, the main root is short, lateral roots are well developed, numerous and dense; root depth 8—16 cm, root spread 20—26 cm.

(4) Branching habit: the branching ability is strong, reaching 76—90 lateral branches. From germination until the appearance of lateral branches, the main stem grows slowly; before late May the stem thickens rapidly; from early to mid-August, the second peak period of bolting occurs; in early September it enters the bud stage and growth stops. Dry leaf weight and artemisinin content increase with the prolongation of the growth period.

(5) Flowering habit: mid-September is the beginning of the flowering period, late September is the full flowering period, and the end of late September is the end of flowering. The flowering order is from bottom to top, on the same branch opening from the stem upward, and on the same inflorescence opening from the outside inward. The flowers are tubular, the outer ones all female flowers, the central ones bisexual flowers. The self-pollination rate is 5%, and it is a cross-pollinated plant.

(6) Stress resistance: it has a relatively strong biological competitive ability. After the first branching it grows fast, forming a plant community dominated by sweet wormwood with an overwhelming advantage over weeds. It has relatively strong stress resistance, resistant to drought, resistant to waterlogging, and resistant to phytophthora blight.

2. Requirements for External Conditions

Sweet wormwood is widely distributed, often growing wild in open fields, on hillsides, roadsides, riverbanks, and beside houses. It grows most abundantly in harvested corn fields, rapeseed fields, or land abandoned for two years, less in cultivated land, and least in land abandoned for many years.

(1) Temperature: sweet wormwood has a relatively strong adaptability to temperature. Sweet wormwood grown in the mid-altitude areas of Enshi Prefecture has a relatively high content of active ingredients (artemisinin), while sweet wormwood from the north has a lower content. Sweet wormwood with higher content is mostly distributed in zones of 10.4℃—14.9℃, with accumulated temperature of 4627.2℃—5212.7℃. Seed germination requires alternating temperature; under alternating temperature the germination rate is higher than under constant temperature. At 20℃—27.5℃, bolting and budding grow rapidly, and the increase in active ingredient content is also fast.

(2) Water: from bolting to the budding stage, the average precipitation is best at around 200 mm, and the relative humidity is best at 80%. It grows vigorously in high-temperature and high-humidity zones.

(3) Sunlight: with a temperature of 30℃, light intensity of 1000—2000 lux, and photoperiod of 12:12 hours, it best promotes early maturity of sweet wormwood, with high and stable active ingredient content. During the branching to budding stage the sunshine hours are relatively long, at 156.5—169.4 hours/month, and during the flowering period the sunshine hours are 185.3 hours/month. Sweet wormwood is a short-day plant, requiring annual sunshine hours of around 1000 hours; too much or too little is unsuitable. If sunshine hours are too many or too few, although sweet wormwood can grow, it will lead to a decrease in artemisinin content.

(4) Soil: for sweet wormwood, it is best to choose sunny and moist alluvial soil or purple-red soil with a parent material of gray thick-bedded limestone of the Permian system. Sweet wormwood grown in yellow loam soil has a relatively low active content and is not suitable for planting.