First, the initial seed collection process:
1. Selecting the right species is crucial. Choose mature bulbs from the field or production area. The selected bulbs should be upright, firm, and smooth, with a clear ratio to their leaves. The pseudostems above the bulbs should be sturdy, not prone to lodging, and free from pests or diseases. After selection, the individual bulbs should be kept separate and protected from rain and direct sunlight.
2. Planting is typically done in mid-September in most parts of Shandong. The goal is to establish new roots and young seedlings before winter. The planting density should be around 5,000 to 6,000 plants per mu, with spacing of 35 cm by 35 cm. When planting, make sure the bulbs are placed slightly deeper, covered with about 3 cm of soil to help them survive the winter and reduce the risk of lodging in the following year. Immediately after planting, water the soil thoroughly, and apply frozen water before winter to maintain proper moisture levels. In early October, apply a single dose of compound fertilizer at 10–15 kg per mu. Before winter arrives, cover the planting holes with grass or organic mulch to protect the bulbs from cold temperatures.
3. Seed management begins when the seedlings turn green again in the following spring. Water them with Qingshui (a type of clean water) and apply nitrogen fertilizer during irrigation. Cultivate the soil 1–2 times to increase ground temperature. Before flowering, manage water and fertilizer carefully to avoid excessive growth that could lead to lodging. After flowering, keep the soil moist and apply one topdressing of compound fertilizer to promote healthy seed development. To prevent wind damage and flower drop, install supports. If the weather is rainy or humidity is too high, and the anthers don’t open naturally, manual pollination may be necessary. Onions are also vulnerable to thrips and onion flies, so timely pest control is essential.
4. Harvesting occurs about three weeks after flowering. When a few pods on the top of the bulb begin to turn black and crack, it’s time to harvest. Cut the bulbs, leaving the calyx about 30 cm long, and place them in a well-ventilated area to allow the seeds to fully mature. One week later, remove the flowers, dry the material, thresh it, and store the seeds properly.
Second, secondary seed collection: When harvesting the first batch of bulbs, take care not to step on the wounds or pull out the mother bulbs. After collection, leave the mother bulbs in the field during summer. Avoid weeding and do not cut off any remaining flower buds to provide shade and reduce heat stress. Water lightly when the soil is dry to prevent the bulbs from shrinking. Drain excess water after heavy rains to avoid rotting.
In the fall, once the mother bulbs start sprouting, clean the field, remove weeds and flower buds, and loosen the soil to encourage germination. Onion bulbs can produce 3–4 scale buds, forming 3–4 new bulbs. During the calyx growth stage, small bulblets develop at the base of each calyx, containing 3–4 scale buds. After germinating in autumn, these will grow into 3–4 new mother bulbs. Water regularly in autumn to keep the soil moist and apply compound fertilizer at 15 kg per mu during irrigation. Monitor for pests and follow standard seed collection practices. In the following spring, the number of pollen aspirates can be 3–4 times higher than in conventional methods, leading to more than double the seed yield. This two-year seed collection method reduces costs, shortens the cycle, ensures quality, and increases output.
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