First, scientific fertilization. The first round of fertilization should be done after the return of spring to support the growth of the onion root system and lay a solid foundation for the development of the above-ground parts. It is recommended to use fully decomposed organic manure at a rate of 1,000 kg per 667 square meters, combined with 20 kg of superphosphate and 10 kg of potassium sulfate. For fields using mulch film, apply about 15 kg of diammonium phosphate and 10 kg of potassium sulfate per 667 square meters.
When the onion plants have developed 8 to 10 true leaves and the bulb starts to form, it's time to apply the "bulb fertilizer" in two or three stages. A dosage of 10-20 kg of ammonium sulfate per square meter is generally effective. Fertilization should occur during the period of bulb expansion, and the amount must be carefully controlled. Avoid excessive nitrogen application when the bulb begins to swell, as this can lead to "luxury consumption," where the plant grows too vigorously and becomes weak. During this phase, adding 5-10 kg of potassium sulfate per 667 square meters helps improve bulb storage stability, as potassium deficiency can reduce the quality and longevity of stored onions.
Second, timely watering. After planting onions in winter, it's important to water them back to Qingshui (a term referring to a specific watering stage) in spring. Watering too early can lower soil temperature, which is not ideal for onion growth and may cause leaf tip burn or stunted growth. The timing of irrigation should be adjusted based on soil type, weather conditions, and plant development. In sandy soils or dry climates, the seedling stage should be shorter, while in clay soils or during rainy seasons, it should be extended to encourage proper bulb formation. This process usually takes around 10 days. Signs that the seedling stage is ending include dark green, thickened leaves with increased waxy coating and darker heart leaves. After this stage, water every five days to promote bulb expansion. If plants begin to fall over, stop watering to prevent damage during storage.
Third, soil cultivation. Before the seedlings emerge, especially in non-mulched fields, regular cultivation is essential. Soils with higher viscosity require more frequent tilling compared to sandy soils. The depth of cultivation should not exceed 3 cm—shallow near the plants and deeper further away. Once ridges are formed, stop cultivating. Midway through the process, you can also perform earthing up to help support the plants and improve drainage.
Fourth, harvesting and storage. In southern Shandong, onions are typically harvested in mid-June. The main signs of maturity include the absence of new leaves filling the leaf sheaths, hollow pseudo-stems, and the plants falling over at the base. The timing of harvest depends on the variety, planting date, and local climate. Varieties with short dormancy and poor storage qualities should be harvested earlier. When about half of the plants have fallen, it’s time to start harvesting. For late-maturing varieties, wait until 70% of the plants are lodged before beginning the harvest.
Harvesting should be done on sunny days, ideally after several consecutive sunny days. Pull the entire plant out and spread it out for 2–3 days to dry. During drying, only the leaves should be exposed to air—not direct sunlight. Cover the bulbs with leaves to help them mature and dry their outer skin. Afterward, remove any soil and trim off the fibrous roots and dead leaves before storing. Some farmers choose not to remove the leaves and instead bundle or tie the onions directly for storage.
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