Short-Day vs Long-Day Onions: Which to Grow

Verdict first: if you garden in the southern US, roughly below the 35th parallel (a line through Memphis, Oklahoma City and Albuquerque), grow short-day onions; if you’re north of about the 37th parallel (St. Louis, Denver, Richmond and up), grow long-day onions; if you’re in between, or unsure, grow intermediate-day onions such as Candy, which bulb across a wide band of the country. Planting the wrong type is the most common reason onions stay small or bolt. Onions decide when to stop growing leaves and start forming a bulb based on how many hours of daylight they get, so matching type to latitude is the single most important choice you make.

Part of our Vegetable Gardening & Raised Beds guide →

In this guide

1. Side-by-Side Comparison
2. How Day Length Controls Bulbing
3. Short-Day Onions
4. Intermediate-Day Onions (Including Candy)
5. Long-Day Onions
6. Decision Factors
7. Regional Planting Guide
8. Common Mistakes
9. Growing Tips for Any Type
10. Which Should You Choose?
11. Frequently Asked Questions

Side-by-Side Comparison

Factor	Short-day	Intermediate-day	Long-day
Day length to bulb	About 10 to 12 hours	About 12 to 14 hours	About 14 to 16 hours
Best US latitude	South of about 35°N	Roughly 32°N to 42°N	North of about 37°N
Typical planting	Fall to winter (Oct to Jan)	Fall in the South, early spring farther north	Early spring, as soon as soil is workable
Typical harvest	Late spring	Early to mid summer	Mid to late summer
Flavor	Mostly mild and sweet	Sweet to mild	Sweet to pungent
Storage	Short, often weeks to a few months	Moderate	Many varieties store for months
Example varieties	Texas 1015Y, Yellow Granex, Red Creole, Southern Belle	Candy, Red Candy Apple, Super Star, Sierra Blanca	Walla Walla, Yellow Sweet Spanish, Copra, Redwing, Ailsa Craig

How Day Length Controls Bulbing

An onion spends its early life growing leaves. Each leaf corresponds to a ring in the eventual bulb, so more and bigger leaves before bulbing mean a bigger onion. When daylight reaches a threshold for that variety, the plant switches from leaf growth to bulb formation. It stops making new leaves, and food from the existing leaves swells the bulb.

That’s why timing and type must match. In the South, winter days are short and summer days never get as long as they do in the North. A short-day onion planted in fall grows leaves through the mild winter, then bulbs as spring days pass about 10 to 12 hours. A long-day onion in the same garden might never get the 14 to 16 hours it needs, so it keeps growing leaves and makes a thick neck rather than a bulb. In the North, where June days run 15 hours or more, a short-day onion planted in spring hits its trigger almost immediately, before it has grown many leaves, and makes a small bulb. Our guide to why onions stay small covers this and the other common causes.

Short-Day Onions

Short-day onions are the classic southern sweet onions. Vidalia onions in Georgia are short-day Granex types, and the Texas 1015Y, a Grano type, is famous in Texas. They’re planted as transplants or sets in fall or early winter, from about October in the Gulf states into January in some areas, and harvested in late spring.

• Strengths: Large, mild, sweet bulbs; early harvest before southern summer heat.
• Weaknesses: High water and sugar content means short storage; can bolt if a cold snap follows a warm spell after plants are already sizable.
• Varieties: Texas 1015Y (Texas Early Grano types), Yellow Granex, White Bermuda, Red Creole, Southern Belle Red.

Intermediate-Day Onions (Including Candy)

Intermediate-day onions, sometimes sold as day-neutral, begin bulbing at about 12 to 14 hours of daylight. That makes them the most forgiving type and the best choice if you live in the transition belt from roughly the Carolinas across Tennessee, Arkansas, Oklahoma and into Kansas and parts of California, or if you’re simply unsure. Candy is the best-known variety, a large, sweet yellow onion that also stores reasonably well. Candy onion plants are widely sold as bundles of transplants.

• Strengths: Adaptable across much of the country; sweet flavor with better storage than most short-day types.
• Weaknesses: At the far north or far south, a true short- or long-day variety usually performs better.
• Varieties: Candy, Red Candy Apple, Super Star (white), Sierra Blanca, Cabernet (red).

Long-Day Onions

Long-day onions are the northern standards. They’re planted in early spring, often four to six weeks before the last frost, since onions tolerate light frost. They grow leaves through spring and bulb as days stretch toward the summer solstice, then mature in mid to late summer.

• Strengths: Many varieties store for months; the widest range of flavors from sweet Walla Walla to pungent keepers.
• Weaknesses: Won’t bulb properly in the South; need a long, steady growing season.
• Varieties: Walla Walla (sweet, short storage), Yellow Sweet Spanish, Ailsa Craig (very large), Copra and Patterson (storage), Redwing (red storage).

Decision Factors

Latitude

Look up your latitude using a map or your phone’s location. Below about 35°N, choose short-day; above about 37°N, choose long-day; between, choose intermediate or test both. Coastal and high-elevation areas can shift the picture slightly because temperature also affects growth, so ask a local extension office or nursery which varieties do best near you.

Storage needs

If you want onions to last into winter, long-day storage varieties are the best keepers. Sweet short-day onions are best eaten fresh within weeks to a few months. Our guides on curing onions and storing them explain how to stretch shelf life for any type.

Flavor

Sweetness in onions has a lot to do with low pungency, which is influenced by variety and by soil sulfur. Short-day and intermediate onions are mostly mild; long-day onions range from sweet to strongly pungent. Pungent onions are often the best keepers.

Season length and heat

Day length isn’t the only clock. Onions grow best in cool weather and mature as heat builds. In the South, short-day onions planted in fall finish before summer heat stresses them; trying to grow them through a southern summer is a losing battle. In the North, long-day onions need the full spring and early summer to build leaves, so get them in the ground as early as the soil can be worked. In short-season mountain areas, start seed indoors in late winter or buy transplants to gain several weeks.

Planting format

Onions can be grown from seed, sets (small dormant bulbs) or transplants (bundles of young plants). Transplants are the most reliable way to get a specific day-length type, since they’re sold labeled by type and timed for your region. Sets are convenient but often unlabeled for day length and more prone to bolting. Our comparison of onion sets vs seeds covers the trade-offs.

Regional Planting Guide

Region (examples)	Onion type	Typical planting window
Gulf Coast, Florida, south Texas	Short-day	October to January
Low desert Arizona, Southern California	Short-day	October to December
Georgia, Alabama, the Carolinas lowlands	Short-day or intermediate	Fall to late winter
Tennessee, Arkansas, Oklahoma, Virginia	Intermediate	Late winter to early spring
Kansas, Missouri, Kentucky	Intermediate or long-day	Early spring
Northeast, Great Lakes, northern Plains, Northwest	Long-day	Early spring, 4 to 6 weeks before last frost

Common Mistakes

• Buying unlabeled sets: Generic yellow, white or red sets at the hardware store may not suit your day length. Look for the type on the label or buy named transplants.
• Planting too late: Late planting shortens the leaf-growing phase before the bulbing trigger, giving small bulbs regardless of type.
• Planting oversized sets or transplants in fall: Large plants that experience a cold spell can be triggered to flower. Pencil-thick transplants are the sweet spot. Our article on why onions bolt explains the cold trigger.
• Feeding nitrogen late: Heavy nitrogen once bulbs are forming leads to thick necks and poor storage.
• Harvesting too soon: Wait until most tops have fallen over naturally and begun to dry before lifting for curing.

Growing Tips for Any Type

• Plant early: The more leaves an onion grows before its bulbing trigger, the bigger the bulb.
• Spacing: Set transplants about 4 to 6 inches apart in rows 12 to 18 inches apart; closer spacing yields smaller bulbs.
• Depth: Plant transplants about 1 inch deep; deeper planting can produce elongated bulbs.
• Feed nitrogen early: Side-dress with nitrogen during leaf growth and stop once bulbs begin to swell.
• Water evenly: Onions have shallow roots; keep soil consistently moist, about an inch a week, and taper off as tops begin to fall.
• Weed carefully: Onions compete poorly with weeds; mulch and shallow hoeing help.

Our full guide on how to grow onions covers soil prep, feeding schedules and harvest in detail, and the vegetable gardening guide helps you fit onions into a broader plan.

Which Should You Choose?

• If you live in the Deep South, Gulf Coast, southern Texas, Arizona or Southern California, choose short-day onions and plant in fall or winter.
• If you live in the northern states or Canada border region, choose long-day onions and plant in early spring.
• If you’re in the middle of the country or unsure of your latitude, choose intermediate-day onions such as Candy.
• If you want onions that store into winter, lean toward long-day storage varieties where your latitude allows.
• If you want big sweet onions for fresh eating, choose short-day sweet types in the South, Candy in the middle, or Walla Walla in the North.