How to prevent premature bolting in onion cultivation

Causes of premature bolting in onions When the seedling stem diameter is greater than 0.6 cm, under conditions of 2°C~5°C for 60~70 days, the onion can complete flower bud differentiation. When the stem diameter exceeds 0.9 cm, the onion's ability to perceive low temperatures increases, and the low-temperature time required for vernalization is correspondingly shortened. When the outside temperature rises and the daylight hours lengthen, the onion can bolt and flower.

Different varieties have different abilities to perceive low temperatures, and the number of days required for vernalization also varies. Generally, southern varieties can complete vernalization after 40~60 days at 2°C~5°C, while northern varieties under the same low-temperature conditions require 100~130 days for vernalization. The degree to which onions perceive low temperatures is also related to factors such as fertilizer, soil moisture and sunlight. Conditions such as fertilizer deficiency, drought and weak light easily induce flower bud differentiation in onions, resulting in premature bolting. Measures to prevent premature bolting in onions Select excellent varieties with strong winter hardiness, slow response to low temperatures and resistance to bolting. This is an important measure for controlling premature bolting. Choose northern-type varieties whenever possible; generally, red-skinned onions bolt prematurely less than white-skinned onions. When introducing varieties, bolting generally does not easily occur when introducing from high latitudes to low latitudes, but bolting easily occurs when introducing from low latitudes to high latitudes. Choose a suitable sowing date and planting date Choosing an appropriate sowing date is the most effective measure for preventing premature bolting in onions. With early sowing, the seedlings easily form large seedlings before winter that can pass through vernalization, and the bolting rate after spring begins is high. However, if sowing is too late, the seedlings are too thin and weak, reducing cold resistance and ultimately affecting yield. With timely sowing, the seedlings are smaller and will not bolt prematurely the following spring. Strictly control fertilizer and water during the seedling stage Before winter, do not apply too much fertilizer; apply light fertilizer and water later to promote robust seedling growth. For larger seedlings, control irrigation and fertilization. After spring warms up, strengthen fertilizer and water management. If bolting has already occurred, the method of removing the bolt can be used; when the swollen part of the bolt emerges, remove it, and a certain yield can still be obtained. Master the appropriate sowing rate Generally maintain a nutritional area of 4~5 sq cm per plant in the seedbed, to prevent the seedlings from being too dense and growing thin and weak, and also to prevent the formation of large seedlings due to excessive nutritional area. Use hormones to control bolting Spray 0.25% ethephon or 0.16% maleic hydrazide during the seedling stage or after flower bud differentiation, which has a certain effect on inhibiting premature bolting.