(1) vegetative growth period ① germination period. The germination period is from seed germination to the appearance of the first real leaf. Onion seed coat is hard and difficult to absorb water, so it germinates slowly. Under suitable conditions, it takes about 10 ~ 15 days to be unearthed after sowing. During this period, the soil should be kept moist, sowing should not be too deep and covering soil should not be too thick.
② Seedling stage. From the first true leaf to the seedling stage. The length of seedling stage is related to sowing and planting season. Sow autumn seeds in autumn, and the seedling stage is about 50 ~ 60 days; Sow spring seeds in autumn, the seedlings can grow for about 60 ~ 80 days before winter, and the wintering period is 120 ~ 150 days; Sow spring seeds in spring, and the seedling stage is about 60 days. The absolute growth of onion seedlings after excavation is not large, especially within 1 month after excavation, with small, tender leaves and thin mesophyll. At this time, it is necessary to maintain appropriate temperature and humidity to promote its growth, especially the growth of roots. When the onion seedlings grow to a certain size, they should be planted in the ground in time. At this time, the weight of each seedling should be about 5-6 grams, the stem diameter should be 0.6-0.8 cm, the plant height should be 20 cm, and there should be 3-4 real leaves. The seedlings are too big, and it is easy to bolt prematurely. During the overwintering period after planting, the growth of onion is very small. Therefore, fertilizer and water should be well controlled before winter to prevent the accumulation of dry matter from being too fast and too prosperous, and reduce the overwintering ability of plants. At the same time, because the plants are too big to feel the low temperature, it is also necessary to prevent early bolting in the next spring.
③ vigorous growth period. After the onion turns green, it belongs to the vigorous growth period until the bulb expands. At this time, the environmental temperature rises, the onion grows faster, and the underground part is sensitive to temperature. The growth rate in the early stage is faster than that in the aboveground part. Later, the growth of aboveground parts gradually accelerated, the number of green leaves increased, and the leaf area expanded sharply. With the vigorous growth of leaves, the base of leaf sheath thickens, and bulbs begin to expand slowly, forming small bulbs mainly in the longitudinal direction. During this period, the leaves mainly grew rapidly, and the number of leaves increased from the initial 4-5 to 8-9, lasting about 40-50 days. During this period, it is necessary to ensure sufficient water and fertilizer supply, promote the vigorous growth of aboveground parts, and lay a solid foundation for the expansion of bulbs. In the later stage, water and fertilizer should be controlled to prevent the overground part from being greedy for green and delay the bulb expansion.
④ Bulb expansion stage. Bulb expansion period starts from the base of leaf sheath to mature bulb harvesting, which lasts about 30 days. After the end of leaf growth period, plants accumulated a lot of assimilates in leaf sheaths. With the high temperature of 20 ~ 26℃ and the arrival of sunshine with a short duration of 13 ~ 15, the growth of leaves was inhibited, and assimilates in leaves and leaf sheaths began to transfer to the base of leaf sheaths, which accelerated the expansion of leaf sheaths to form bulbs. When the bulb expands to a certain extent, the leaves begin to turn yellow, the pseudostem loses water and becomes soft, lodging occurs, and physiological activities gradually slow down. Nutrients in 1 ~ 3 scales outside the bulb transfer to the inside and become leather-like, which is a sign that onions are dormant and should be harvested in time. If you encounter abnormal low temperature or excessive application of nitrogen fertilizer during the bulb expansion period, the leaves will grow greedily and will not lodging. (2) Physiological dormancy period Onion bulbs enter physiological dormancy period after harvesting. This is the result of onion's long-term adaptation to high temperature and drought conditions in summer. Dormancy period is related to variety characteristics, storage conditions and dormancy degree, generally 60 ~ 90 days. In order to facilitate storage, harvested onion bulbs should be air-dried immediately to promote their physiological dormancy. During this period, even given good germination conditions, bulbs will not germinate. Onions can germinate normally only after dormancy is over and placed in a suitable environment. (3) Reproductive growth period ① flower bud differentiation period. The flower bud differentiation period starts from the growth cone to the flower bud elongation bolting. Onion is a low-temperature green vernalization crop. When the seedlings grow to a certain size, after a certain period of low temperature, the growth cone will stop differentiating into leaf buds and differentiate into flower buds through vernalization.
② bolting and flowering period. The bolting and flowering period is from the end of flower bud differentiation to the end of pollination and fertilization of the first bloom flower on the inflorescence. Plants or bulbs with differentiated flower buds can bolt, blossom and bear fruit under the conditions of high temperature and long sunshine in the growing place, and complete the whole growth process. Generally, 2 ~ 5 flower buds can grow from each bulb, and 1 spherical umbel is planted at the top of each flower bud. The flowering period of each inflorescence is 10 ~ 15 days, and the flowering period of the whole plant can last about 1 month.
③ Seed formation period. The seed formation period of onion is from flowering to seed maturity. It will take about 25 days. Generally, when the temperature is high, the seeds mature quickly, but the plumpness is poor. When the temperature is low, the seeds mature slowly and the plumpness is high.