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Onion's Bolting/Flowering - Solution Guide

Onion's flowering or bolting, as it is referred to, is not variety-specific, nor is it a universal phenomenon with onion crops. It can be a regional issue though, as it is caused due to plant stress, which is primarily weather related.

Onions bolt or bloom when they are subjected to cold temperatures or fluctuations in temperature after they are planted.

To avoid bolting, proper planting times will matter greatly.
Onions are a cool-season crop, but they are biennials, which means they can be fooled into a reproductive stage (flowering) from adverse conditions after they are planted. This is normal plant behavior, unfortunately.

Onions should be planted early, about 4-6 weeks before the last average frost date. However, if they are planted too early, and colder temperatures occur, that can stimulate them to bolt. Other factors like nutritional imbalances and moisture stress can also lead to bolting, but primarily it is due to a physical response to temperature.

After they are planted, if the local weather patterns are unsettled or produce inconsistent temperature swings, mulching over newly planted onion rows may help blanket them and keep soil temps more consistent, which can help avoid issues with bolting.
Maintain consistent moisture.
Have a soil test done to ensure no nutritional imbalance is to blame.
Onions are considered heavy feeders, but if nitrogen levels go too high, it can interfere with their proper growth and development.