Onion is one of the most challenging vegetables to store during winter. While traditional storage methods like temperature control and natural cold storage can be effective, proper environmental management is key to ensuring long-term preservation and meeting market demands throughout the season.
Green onions are particularly resilient to low temperatures, withstanding as low as -20°C. When frozen at this temperature, they can gradually thaw at 0°C or above without losing cellular viability, making them well-suited for low-temperature storage. The ideal conditions for this method are around 0°C with a relative humidity of 85% to 90%. For micro-freezing, a slightly lower temperature range of -3°C to -5°C is recommended. If no cold storage is available, green onions can still be stored at room temperature for a short period, provided the humidity remains around 80%. However, high humidity increases the risk of spoilage.
For long-term storage, it's essential to choose varieties with high soluble solids content and harvest them at the right time. Early harvesting can reduce storage stability. There are several effective storage methods commonly used:
1. **Rack Storage**: This method is ideal for small spaces and long-term storage. Wooden poles or steel structures are arranged into 2–3 levels, each about 80 cm high. Dried green onions are bundled in groups of 7–10 kg and placed on the shelves, leaving space between them for ventilation. The area should be covered with tarpaulin or straw to protect against rain and snow. Regular inspections are necessary to remove any spoiled bulbs.
2. **Flatland Storage**: A layer of dry sand, about 3–4 cm thick, is spread on a shaded flat surface. Green onions are tightly packed with their roots downward, forming rows 1.5 meters wide. After arranging, a 15 cm layer of sand is added around the roots. Once the onions are cool and slightly frozen, they are covered with straw or cloth to protect from rain and sun.
3. **Shallow Trench Storage**: A shallow ditch, 20–30 cm deep and 50–70 cm wide, is dug in a cool, ventilated area. Bundled green onions, weighing around 10 kg, are placed into the trench. Corn stalks are arranged around the bundles to help maintain a cool environment below 0°C. The top is then covered with grass or straw curtains.
4. **Kiln Storage**: After drying for a few days, green onions are bundled and placed in a dry, sunny, and sheltered location to further dry. When temperatures drop, they are moved into a kiln. The kiln must maintain a low temperature of around 0°C, while also controlling heat and moisture.
5. **Cold Storage**: Pest-free, non-damaged green onions are tied into 10 kg bundles and placed in boxes or baskets. They are stored in refrigerated areas at 0–1°C with 80–85% humidity. Regular checks are required to remove any spoiled onions promptly.
No matter which storage method is used, maintaining a stable, low temperature is crucial. Avoiding repeated freezing and thawing helps preserve quality and minimize losses. With proper care and attention, green onions can remain fresh and market-ready throughout the winter season.
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