When is the best time to plant Isatis root?

Isatis root , also known as woad, big blue or indigo root, is an annual or biennial herb belonging to the cruciferous family. The plant height is approximately 33 to 66 cm and the stem diameter is 5 to 8 mm. It has an erect stem and many branches. The leaves are alternate. The basal leaves are larger, 3.5 to 11 cm long and 0.5 to 3 cm wide. The apex is obtuse, the base is arrow-shaped, the margin is entire or has inconspicuous serrations, and there are petioles. The leaves are oblong-elliptic, terminal or axillary, the flowers are small and yellow, about 3 to 4 mm in diameter, without bracts, and the pedicels are slender. The fruit is an oblong silique, flat and winged.

The root of Isatis indigotica is white, slender and cylindrical. In terms of medicinal use, the roots and leaves of Isatis indigotica are used as different medicinal materials respectively. The root is Isatis indigotica and the leaves are called Isatis indigotica . Usually the roots and leaves can be harvested in the year of planting, and the plant will bloom and bear fruit in May of the following year. Isatis root is grown in more than 20 provinces and cities in my country, especially in Hebei, Henan, Shandong, Shanxi and Hubei. So when is the best time to plant Isatis root?

1. Planting Season

The planting of Isatis root can be divided into four stages: autumn sowing, early spring sowing, spring sowing and summer sowing. The main purpose of autumn sowing and early spring sowing is to harvest seeds. The roots of Isatis indigotica during these two periods are not suitable for use as medicinal materials. Summer sowing is mainly suitable for areas in the south with a longer rainy season. It helps reduce pests and diseases, but the yield is relatively low. Spring-sown isatis root can be harvested as both leaves and roots, and has a high yield, making it the most common planting method.

2. Preparation before sowing

Isatis root is a deep-rooted plant that prefers a cool environment. It is relatively cold-resistant and afraid of waterlogging. It is suitable for planting in North China and Northwest China. The preparation work before sowing mainly includes site selection, land preparation and fertilization.

1. Site selection

Isatis root is suitable for planting in sandy loam or river alluvial loam with low groundwater level, good drainage, loose and fertile. Clay and low-lying, waterlogged land should be avoided. It is best to choose a place that is sheltered from the wind, sunny, and close to a water source. The previous crop should be beans or corn. If it is a slope, the slope should not exceed 15°, and drainage facilities must be well equipped.

2. Fertilization and land preparation

The best base fertilizer is well-rotted livestock manure, and avoid using raw manure. To prevent and control pests, spray 800 times diluted 90% dichlorodiphenyltrichloroethane and mix well during the manure stacking process. Apply 2000-3000 kg of base fertilizer per mu. If there is sufficient manure, it can be increased to 4000 kg. If manure is insufficient, add 50 kg of diammonium phosphate or superphosphate and 15 kg of potassium chloride or potassium sulfate. Deeply till the soil to a depth of more than 30 cm to facilitate root growth. After land preparation, flat ridges can be made in the north, while high ridges should be made in the south to facilitate drainage.

3. Sowing

1. Seed selection

Choose new seeds harvested the previous year with black seed coats. Such seeds are well mature and have a high germination rate.

2. Seed treatment

Soak the seeds in clean water for 12-24 hours to remove grass clippings and barren seeds and soften the seed coat to facilitate germination.

3. Sowing time

Spring-sown isatis root is generally sown in early April in the northern region, and can be sown earlier in the southern region, but it must be sown when the local temperature is stable at above 12℃.

4. Planting seeds

Water thoroughly one week before sowing to ensure that the seeds have the moisture they need to germinate and take root. The row spacing for row sowing is 30 cm, and the sowing rate is about 3 kg per mu; the row spacing for hole sowing is 30×20 cm or 30×30 cm, and the seed rate is 1.5-2 kg per mu. The sowing depth is 3 cm, covered with a layer of fine soil, about 1 cm thick, and finally covered with plastic film to keep it moist.

4. Seedling Management

Isatis root seeds will germinate 7 to 10 days after sowing, and all the seedlings will emerge in 15 days. Seedling management work includes piercing holes for ventilation, weeding, thinning, loosening the soil, determining the number of seedlings and applying fertilizer.

5. Field Management

In the daily management of Isatis root, tillage, weeding and topdressing of fertilizers are important tasks. Intertillage and weeding are performed about 4 to 6 times, starting with shallow tillage and gradually deepening as the plants grow. In addition to base fertilizer and urea after transplanting, three more applications of chemical fertilizer are required.

VI. Pest and disease control

The main diseases of Isatis root are downy mildew and powdery mildew, and the main insect pests are cabbage looper and peach bud. Prevention and control methods include paying attention to drainage and ventilation and light transmission, avoiding continuous cropping or crop rotation with crops susceptible to downy mildew, and using 70% mancozeb spray for prevention and control during the disease period, spraying once every 7 days for 2 consecutive times. Methods for prevention and control of powdery mildew include preventing water accumulation in the field, planting at a reasonable density, and applying nitrogen, phosphorus, and potassium fertilizers. In the early stage of the disease, spray 300-500 times diluted 65% zinc ziram wettable powder.

7. Leaf Harvesting

The leaves of spring-sown Isatis root can be harvested for the first time around mid-June. After harvesting, it should be transported out of the planting area as soon as possible for drying. The laying thickness should be 3-5 cm in autumn, and it should be turned over 2-3 times a day. After drying for 2-3 days, gently unfold the leaves while they are still soft, tie them into small bundles with ropes, each bundle weighing about 50 grams, and then hang them on a rope in a cool place to dry for 1-2 days.

8. Harvesting, processing and storage of roots

The harvesting time of Isatis root is slightly different in the north and south. In the north, it is best to harvest it between late October and early November, and in the south, it is best to harvest it in early December after the first frost. Be careful not to cut the roots when digging. Generally, 300-500 kg of fresh roots can be harvested per 667 square meters. Wash the dirt off the dug out Isatis root, remove the reed head, spread it out to dry until it is 70% to 80% dry, tie it into small bundles and then sun-dry it. This is the medicinal "Isatis root". The best commercial isatis root products are those that are long, straight, thick, firm and powdery. Isatis root and isatis indigotica leaf should be stored in a dry and ventilated place. The suitable temperature should be below 28℃, the relative humidity should be 65% to 75%, and the safe moisture content of the product should be 11% to 13%.

To sum up, the soil requirements for Isatis root cultivation are quite special. It needs deep, loose and fertile soil, good drainage, high organic matter content, good air permeability, and appropriate soil pH value. These conditions together provide a good foundation for the growth of Isatis root.