One of the easiest to grow spring vegetable crops is onions. Plant them now while the weather is cool and before long you’ll be enjoying your first harvest of green onions and the big onions will only be a few months away.
First, some terminology. Onions are a biennial plant. That means they start from seed during year one, grow through that season, go dormant, live through the following winter and then reemerge in the second season to continue growth, eventually flowering and producing seed before they die. Their life cycle takes two years to complete.
Onion plants are just starting their first year of life. Onion sets are on year two.
So, is that important? The simple answer is yes. Knowing that onions biennial plants, and that onion plants are in year one and life and onion sets are in year two explains some of what we see in crops that we grow.
Onion plants are just what they sound like, young onion plants. They are planted from seed and then allowed to grow for about 6-8 weeks before being harvested as young transplants. Once replanted, they resume growth, eventually maturing out into large bulbs. Plants can be pulled earlier if small green onions are desired. Sweet varieties of onions are planted this way. Popular varieties include Candy, Texas 1015’s and Yellow Granex. (Yellow Granex is the variety that is planted to produce the popular Vidalia onion. Although this variety makes Vidalia, GA famous for their onions, give Candy a try. It is a better producing sweet onion for our area.) Use onion plants for producing the big onion bulbs.
Onion sets are dormant onion bulbs that are in in their second year of growth when your purchase them. They tend to be hotter varieties which allows them to store better. They are usually just packaged up as red, yellow or white without any variety names. They provide a quick start in the spring and are frequently grown for early crops of green onions but they can also be allowed to mature out and form big bulbs. Because sets planting in the garden are growing in their second year, it is very common for some of them to begin flowering, or bolt, preventing good bulb formation. The larger sets are especially prone to that, so sort your sets out before planting, saving the largest ones for pulling as green onions and the smaller ones for growing on into large bulbs.
So, if onions are biennial plants and onion sets are already one year old when you plant them, why don’t all onion sets produce flowers?
Most varieties that are grown have been selected for the tendency not to flower. That allows for good bulb formation. Also, some onion sets are heat treated before they are sold to prevent flowering. Storing the sets at warmer temperatures for a long enough period of time prevents most of the onions from flowering. If you do get onions that produce a flower stalk, go ahead and harvest it for use. It won’t grow any bigger at that point and it won’t store well.
One last thing about sets. Since they are hotter varieties, they store better than the sweet varieties.
One last growing tip. Onions need to be planted early and then fertilized regularly to produce large bulbs. Plant them in rich soils and fertilize at planting and then every few weeks with high nitrogen fertilizer until they start to bulb. This is the key to producing large bulbs.
We have lots of both on hand, and it’s time to plant if your hoping to be eating fresh onions from the garden this spring.