Kale, a variety of *Brassica oleracea*, is originally from the Mediterranean coast of Greece and has been cultivated in Europe and the United States for centuries. In recent years, it has been introduced from countries like the U.S., Netherlands, and Germany, and is now grown as a specialty vegetable in suburban areas of cities such as Beijing and Shanghai. Known for its strong adaptability, kale can withstand cold, heat, and water stress, making it easy to grow. It can be harvested multiple times in a single growing season, with a harvest period lasting up to six months. Kale thrives in most regions of the country and features unique leaf shapes with feathery, deeply cut edges. Its colorful varieties are highly ornamental and are often used in potted plants or planted along roadsides and in flower beds to enhance the environment.
**Botanical Characteristics**
Kale has underdeveloped main roots with many fibrous roots, typically found in soil layers around 30 cm deep. The stems are erect, fleshy, and thick, reaching heights of 40 to 80 cm. Leaves are green, long-oval, with pinnate divisions on the edges, and vary in thickness depending on the variety. Petioles are relatively long, about one-third the length of the entire leaf. Flowers are yellow and arranged in racemes, while the fruit is a pod containing spherical, brown to dark brown seeds weighing 3–4 grams.
**Growing Conditions**
1. **Temperature**
Kale is adaptable to both warm and cold climates. Seeds germinate slowly at 3–5°C but sprout fastest at 20–25°C. Germination is inhibited above 30°C. Optimal growth occurs at 18–20°C during the day and 8–10°C at night, though it can tolerate temperatures as low as -4°C. It can survive short frosts and continues to grow after temperatures rise. It also tolerates high temperatures (30–35°C), although leaves become fibrous and less tender.
2. **Light**
Kale is a long-day crop that requires sufficient light during vegetative growth before vernalization. Longer days and stronger light promote healthy growth, but too much light during the product formation stage can cause premature aging and reduce flavor quality.
3. **Moisture**
Kale prefers moist conditions, especially during the product formation stage. Soil humidity should be between 75–80%, and air humidity 80–90% for optimal growth. Lack of moisture can severely affect leaf development and yield.
4. **Soil and Nutrients**
Kale grows well in various soils but performs best in loamy, organic-rich soils. It prefers slightly acidic to neutral pH and should not be planted in low-lying areas. It is a heavy feeder, requiring adequate nitrogen, phosphorus, potassium, and trace elements throughout the growing season.
**Cultivation Techniques**
1. **Improved Varieties**
Popular varieties include the Osaka, Nagoya, and Finch series, known for their high yield, good taste, and ornamental value. These varieties are suitable for planting in Shandong and northern China, especially in unheated greenhouses.
2. **Planting Season**
In northern regions, kale is planted in spring and autumn in open fields, and in protected areas during winter. Seed rates are approximately 20–25 g per 667 square meters. Planting schedules vary depending on the region and market demand.
3. **Nursery Preparation**
Seedlings are commonly used for transplanting. A nursery bed of 10–15 m² per 667 m² is prepared with 3 kg of decomposed organic fertilizer per square meter. Sowing methods include drilling and broadcasting, with proper watering and temperature control to ensure healthy seedlings.
4. **Fertilization and Planting**
A base fertilizer of 2,000 kg of finely ground organic manure per 667 m² is applied, followed by several top-dressings. Plants are spaced 60 cm apart in rows with 40 cm between plants, totaling about 2,800 plants per 667 m².
5. **Field Management**
After transplanting, the soil is loosened, weeded, and watered appropriately. Drip irrigation is recommended for efficient watering. In winter, protective measures such as mulching are essential to maintain optimal temperatures.
**Pest and Disease Control**
1. **Black Rot**
Caused by bacterial infection, black rot leads to necrotic vascular tissue and dark spots on leaves. Early removal of infected plants and application of copper-based fungicides are effective treatments.
2. **Downy Mildew**
This fungal disease causes white mold and wilting. Fungicides such as triethylaluminum phosphate or chlorothalonil are used for control.
3. **Sclerotinia Rot**
This disease affects the stem base and leaves, causing soft rot and fungal growth. Proper drainage, balanced fertilization, and fungicides like chloroammonium nitrate help manage the disease.
4. **Cabbage Worms**
Biological insecticides diluted at 2,000 times are applied every 7–10 days to control caterpillars and other pests.
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