My onions are forming flower heads. Should I pinch these off or leave them alone? Will I still be able to harvest onions?
Onions that are forming flowers are said to be bolting. This might be due to the fairly cool weather we’ve had. Here is additional information from Iowa State University.
Excerpt:
“Onions will occasionally bolt or produce a flower stalk. Onions bolt as a reaction to cold weather stress. Temperatures under 45 degrees F may cause the onion to bolt when the plant has five or more leaves. Some onions are more or less susceptible to bolting than others and the process is not completely understood. Unfortunately once the onion does bolt, the quality of the onion bulb deteriorates rapidly and it should be harvested and eaten as quickly as possible.”
This community garden page has general information on the phenomenon of bolting. Early planting, mulching, avoiding overfertilizing, and providing consistent watering will all help prevent bolting. Onions respond to cool springs followed by warm weather by bolting. An Oregon State resource on growing onions describes the onion’s development as follows:
“All onions are biennial, meaning that they normally take two years to grow from seed, flower and set seed again.
Onions first grow ‘vegetatively,’ forming roots, leaves and other plant growth. Once these basics are established, the bulb, the part that is generally known as an onion, forms when the day and night lengths reach the proper length for each particular type of onion.
Once an onion bulb forms, there are enough nutrients stored for flowering, or ‘bolting,’ usually occurring during the second year of an onion’s two-year life. Flower formation usually ruins the bulb for harvest as an onion, as the resources of the bulb usually are absorbed to send up the flowering stem.”
You may find this guide to growing onions from the Center for Agroecology at U.C. Santa Cruz helpful. It also mentions temperature in relation to bolting.