Onion Growth Stages & Germination

Seasons

• Two seasons are required for the onion to complete its life cycle from seed germination to seed production. When onion seeds are planted in the spring of the year, they germinate and form storage tissue, which is the bulb, and then go dormant for the winter. The following spring the plant begins a second growth, bolts and forms the scape and umbel, which in turn produces more seeds. After this two-year process, the whole plant dies. For a shorter growth cycle, both seasons may be forced into a single 10-month growth period when the seeds are planted late in the summer and allowed to overwinter. These plants will produce seeds the following year.

First Season

• Seeds germinate most rapidly at temperatures of at least 55 degrees Fahrenheit. As cool-season vegetables, they may germinate at temperatures as low as 35 degrees, but success is limited. Extended daylight hours of 12 to 15 hours encourage bulb formation and plant growth; the layered bulb is comprised of the bases of the leaves. Energy is stored in the bulb in the form of sugars to feed the bulb through the coming winter. This first-season stage may be allowed to continue into the second season, or it may be dug up and used as sets for the following season.

Second Season

• A young set that is either transplanted for growth, or has been allowed to overwinter in the field, begins its second season by throwing up one or more stalks, or scapes. This stalk grows and eventually terminates in an umbel, or flower head. When it blooms and is pollinated, it then grows seeds, and should be harvested before it splits open or "shatters." This process is also called bolting. Onions that are intended for eating should not be allowed to bolt, as the sugar stored in the bulb is used up at this point and the onion is inedible. Bolting is, however, necessary for seed production.

Green Onions

• Green onions are the young, tender onion tops of first-season bulbs of the shallot variety. Shallots and green onions never form very large bulbs. However, growing your own sets from seed is an excellent opportunity to indulge in green onions from any variety. As the seed germinates and green growth reaches 3 inches, cut back the top to within 1 inch. This not only allows you to harvest multiple tops before transplanting, but also encourages the sets to put more effort into bulb production.