How to prevent onions from bolting early

The reason for the early bolting of onion is that when the stem diameter of the seedling is more than 0.6cm, the onion can complete flower bud differentiation after 60-70 days under the condition of 2 ℃ ~ 5 ℃. When the stem diameter is more than 0.9 cm, the ability of onion to feel low temperature is enhanced, and the low temperature time needed to pass vernalization is shortened accordingly. When the external temperature rises and the sunshine time is prolonged, the onion can bolt and blossom.

Different varieties have different ability to feel low temperature, and the days required to pass vernalization are also different. Generally, the vernalization of southern varieties can be completed after 40-60 days under 2 ℃ ~ 5 ℃, while that of northern varieties takes 100-130 days at the same low temperature. The perception of onion to low temperature is also related to fertilizer, soil moisture, sunshine and other factors. Conditions such as lack of fertilizer, drought and low light are easy to induce onion flower bud differentiation and early bolting. Excellent varieties with strong winter, slow response to low temperature and bolting tolerance were selected to prevent onion from bolting in advance. This is an important measure to control early bolting. Northern type varieties should be selected as much as possible. Generally, red onions are less unripe bolting than white onions. Generally speaking, bolting is not easy to occur in introduction from high latitude to low latitude, but bolting is easy to occur in introduction from low latitude to high latitude. Selecting suitable sowing time and planting date is the most effective measure to prevent onion from bolting in advance. Early sowing, the seedlings are easy to form large seedlings that can pass vernalization before winter, and the bolting rate is high after the beginning of spring. But sowing too late, the seedlings are too weak, reduce the cold resistance, and ultimately affect the yield. Sowing at the right time, the seedlings are smaller, and the next spring will not bolting in advance. Strictly control the fertilizer and water in the seedling stage before winter, it is not suitable to apply too much fertilizer, and apply fertilizer and water thinly in the later stage to make the seedlings grow healthily. For larger seedlings, control irrigation and fertilization. After the spring is warm, strengthen the management of fertilizer and water. If there is bolting, you can use the method of bolting, when most of the expansion of the bolting is removed, you can also get a certain yield. Mastering the appropriate sowing rate generally keeps the nutritive area of a single plant in the seedling bed at 4-5 square centimeters to prevent the seedling from growing weakly due to excessive seedling density and to prevent the formation of large seedlings due to excessive nutritional area. Controlling bolting with hormone spraying with 0.25% ethephon or 0.16% penicillin at seedling stage or after flower bud differentiation has a certain effect on inhibiting early bolting.