Welsh onion is a cross-pollinated crop, and without proper seed selection and preservation, it can suffer from degeneration and lose its desirable traits. Therefore, scientific seed selection plays a crucial role in maintaining the quality of Zhangqiu green onions.
When using the winter whole-plant harvesting method in November, farmers visually inspect the fields to identify well-developed plots. These plots are harvested first, and then individual plants with distinct, typical characteristics are selected. The criteria for selecting these plants include long, slender, tight, and pod-free stems. The leaves should be long and lance-shaped, bright green, with sharp tips. The mesophyll is slightly thin, and the tubular leaves are neatly arranged vertically. The spacing between leaves is wide, and the root system is strong. The entire plant must be free of rot and pests. After selection, the seedlings are planted back into the original field. The original field should be isolated, with no other large onion varieties within 1 km, have fertile soil with good drainage and irrigation, and not have been used for growing onions or garlic for more than three years.
Before planting, trenches are dug in a north-south direction, about 20–30 cm deep and 50–60 cm apart. Organic manure (2,000–3,000 kg), 15–20 kg of potassium sulfate, and 20 kg of superphosphate are added to the trench. The soil is then deeply tilled to mix the fertilizer evenly. Before planting, the seedlings are air-dried to reduce the risk of rot. They are planted at a spacing of 6–8 cm, with approximately 15,000 plants per mu. After planting, watering should be delayed. In winter, wheat straw and cow manure are used to cover the plants to protect them from freezing.
In early to mid-March of the following year, the top part of the plant is cut off to promote flower bud development. At the same time, nitrogen fertilizer is applied, and watering is done promptly. Once the flower buds are removed, the field is cleaned by removing any weak or diseased plants. By late May, the seeds begin to mature, but the maturation period varies, so it's best to harvest when about 80% of the seeds on the bulb are ripe. Harvesting is preferably done in the morning or evening. The bulbs are cut with scissors and placed in a dry, ventilated area as soon as possible. When drying, the seeds should be spread on canvas, not directly on concrete floors, to ensure high germination rates. This method typically yields around 50 kg of seeds per mu.
The winter whole-plant planting method has improved the purity of the variety through single-plant selection, but due to the high cost of seed production, the resulting seeds are not suitable for commercial farming and are better used for breeding original strains.
After cutting spring onions and chopping green onions, select healthy, typical plants. Dry them in the field, bundle them in groups of 10–15 kg, and store them in a dry, cool place or dig a 30 cm deep hole in a dry and sheltered area. Place the plants upright in the ditch with roots down, cover them with soil, and add a layer of grass on top. About 10 days before planting in the next year, remove the plants from storage, discard any rotten or soft ones, and cut the top part to leave 20 cm of stem. After 7–10 days of drying, when the leaves grow 5–10 cm, plant them in the field on a sunny day. The field preparation and planting methods are similar to those used for winter planting. Watering should be avoided immediately after planting. Water the first time after one week, and again after the flower buds are removed, applying fertilizer and water promptly.
This seed production method uses winter plant strains that consume nutrients during dormancy, leading to lower yields—about 25 kg per mu—which is suitable for maintaining original strains. This technique works best in cold northern regions.
The "lazy green onion" method involves selecting the best-growing fields and leaving them untouched until June of the following year. Although this method produces a high yield of seeds, it lacks proper selection, which can lead to variety degradation over time. Therefore, it is not recommended for continuous use.
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