If you have ever planted onions only to grow a lackluster harvest of small bulbs, your growing technique may not be the issue. You may have started with the wrong onion.
There are three types of onions, each one better suited for a certain part of the country. If you plant the wrong one, you won’t get much of a harvest.
How Onions Grow
Onions form bulbs in response to daylength. When the number of daylight hours reaches a certain level, onion plants start bulbing, or forming bulbs. Long-day onions need about 14 to 15 hours of daylight to bulb. Short-day onions need 10 hours of daylight. Day-neutral onions form bulbs regardless of daylight hours and produce well in almost any region.
As soon as daylength hits the 10-hour mark, a short-day onion starts forming a bulb. If the top of the plant hasn’t had enough time to grow big and lush, the resulting bulb will be small. Conversely, if you live where daylength never hits 14 hours, long-day onions will never form a bulb. All you’ll get is green leaves.
By choosing the right type of onion for your region, you’ll get healthy green stems that are large enough to fuel forming a fat and tasty bulb.
Choosing the Right Onion for You
Which onion type you should plant depends on where you live.
- In the North (the area north of a line drawn from San Francisco to Washington, D.C.), summer days are long. This region encompasses Zones 6 and colder. If you garden in this area, grow long-day onions.
- In the South, summer days don’t vary as much in length from winter ones. This region includes Zones 7 and warmer. If you garden in this area, grow short-day onions.
- Day-neutral (sometimes called intermediate) onions form bulbs in any zone, but are ideal for gardeners in Zones 5 and 6.
- For a visual representation of onion types broken into most suitable regions, see this map from Dixondale Farms.
Types of Onions
- Form bulbs with 10 to 12 hours of daylight
- Need mild winter climate (Zone 7 or warmer)
- Planted in fall, mature in late spring
- Can be grown in the North, but bulbs don’t get as large
- Matures in 110 days in the South with fall planting, 75 days in the North with spring planting
- Examples: Georgia Sweet, Sweet Red, Texas Super Sweet, Texas Sweet White
- Form bulbs with 12 to 14 hours of daylight
- Produce nice bulbs in all regions except South Florida or South Texas (ideal for Zones 5-6)
- Planted in fall in mild winter climates and in early spring in northern regions
- Very sweet
- Matures in 110 days
- Examples: Candy Onion
- Form bulbs with 14 to 16 hours of daylight
- Typically grown in northern regions (Zone 6 and colder)
- Planted in late winter/early spring
- Matures in 90 to 110 days
- Stores well
- Examples: Walla Walla Sweet, White Sweet Spanish, Yellow Sweet Spanish
When to Plant
You want to tuck onions into soil at the right time to allow them a long growing season for top growth (leaves), which is necessary to yield plump bulbs. In general, follow these planting guidelines:
- Short-day onions: In Zone 7 and warmer, plant in fall, grow through winter, harvest in late spring.
- Long-day onions: In cold regions (Zones 5 and colder), plant in early spring as soon as the ground is workable, and harvest in mid- to late summer. Bulbing is triggered after the summer equinox (June 21) in most northern regions.
- Day-neutral onions: Plant in early spring in colder regions, in fall in warm regions.
The best way to know the right time to plant for your region is to contact your local extension agent. You can find the nearest Extension office through the Cooperative Extension System map.