In the early stages of onion cultivation, scientific fertilization plays a crucial role in ensuring healthy growth. The first round of fertilization should take place after the return of spring to support the development of the root system and lay the foundation for strong above-ground growth. This initial application should consist of 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 covered with mulch, it is recommended to apply 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 bulbs start to swell, it's time to apply the "bulb fertilizer" in two to three applications. A typical dose is 10-20 kg of ammonium sulfate per square meter. Fertilization should be done during the middle phase of bulb expansion. It’s important to control the amount of nitrogen applied, especially when the bulb begins to grow, as excessive nitrogen can cause the plant to become too lush and weak, leading to poor quality. During this stage, adding 5–10 kg of potassium sulfate per 667 square meters helps improve bulb storage stability, as potassium deficiency can lead to poor shelf life.
Watering should be timely and carefully managed. Before winter planting, it’s essential to water onions after the spring thaw. Watering too early can lower soil temperature, which hinders growth and may cause leaf tip burn. When the bulbs begin to expand, the irrigation schedule should be adjusted based on soil type, weather, and plant condition. In sandy soils or dry conditions, the seedling period should be shorter, while in clay or wet areas, it should be extended. This helps promote bulb formation, typically taking around 10 days. The signs that the seedling stage is ending include dark green, thickened leaves with increased waxy coating and deeper heart color. After this, watering every five days helps speed up bulb growth. If plants begin to fall over, watering should stop to prevent moisture retention in the bulbs before harvest.
Soil cultivation is also an important practice. For fields without mulch, cultivation should be done before the seedlings emerge. More frequent cultivation is needed in heavy soils compared to sandy ones. The depth should not exceed 3 cm, with shallow cultivation near the plants and deeper away from them. Once the ridges are formed, cultivation should stop. Earthing up can be done during the process to help support the plants.
Harvesting typically occurs in mid-June in southern Shandong. The main indicators of maturity include the absence of new leaf sheaths filling the bulb, hollow pseudostems, and the plant falling over at the base. The timing of harvest depends on the variety, planting date, and climate. Varieties with short dormancy and poor storage should be harvested earlier. When half of the plants fall, harvesting can begin, while late-maturing varieties should be harvested when about 70% of the plants are lodged.
Harvesting should be done on a sunny day, ideally after a few consecutive sunny days. Pull the entire plant out and spread it for 2–3 days. During drying, only the leaves should be exposed to air, not direct sunlight, and the bulbs should be shaded with leaves to help ripen and dry the outer skin. Afterward, remove the soil, cut off the fibrous roots and dead leaves, and store the onions. Some farmers choose to leave the leaves intact and bundle them for storage.
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