Jacksonville sits at 30.48 degrees north, and on the longest day of the year it gets 13 hours and 58 minutes of daylight. That single number decides which onions will actually form a bulb in a Florida garden and which will just sit there making leaves. Florida stretches across several degrees of latitude, so a gardener in Pensacola and one in Miami are working with different realities even though both live in “Florida” on a map.
How long your longest day is
Onions don’t bulb because of heat, mulch, or fertilizer timing. They bulb because of day length. Each variety carries a genetic trigger: a number of daylight hours that tells the plant to stop pushing out leaves and start swelling a bulb underground. At 30.48N, the longest day of the year tops out at 13 hours and 58 minutes of daylight. That’s the ceiling. Nothing in a north Florida garden will ever see more daylight than that, no matter how you plant it or when.
That ceiling puts north Florida squarely in short-day territory, brushing the edge of intermediate-day range. Short-day onions start bulbing at around 12 hours of daylight, according to Clemson Cooperative Extension’s Home & Garden Information Center, so they’re comfortably covered by nearly 14 hours. Intermediate-day types, which typically need 12 to 14 hours, are right at the margin here. Long-day onions, the kind that need 14 to 16 hours before they’ll even think about bulbing, are a non-starter. That threshold simply never arrives at this latitude.
This is the entire logic of the page, condensed into one fact. A variety bred for the upper Midwest or the Pacific Northwest is chasing a daylight number that Florida’s sky doesn’t produce, not even at the summer solstice. Everything below is detail built on top of that one number.
Florida runs from the panhandle down to the Keys, a span of latitude wide enough to matter. The Jacksonville figure describes north Florida. Someone gardening in Orlando or Tampa is a few degrees further south, and someone in Miami is further still. The daylight hours only get shorter as you move south, which actually reinforces the same conclusion: south Florida is even more solidly short-day country than the panhandle. If you’re near the state’s northern edge, close to the Georgia line, it’s worth checking your own latitude, since that’s the direction where intermediate-day types start to become plausible.
Which varieties bulb in Florida
Seven varieties documented on this site have a published latitude range that actually covers 30.48N, meaning their catalogue data lines up with what north Florida’s daylight can deliver. All seven are short-day types, which fits the math above exactly.
- Gabriella (short-day, 20-35N)
- Madalyn (short-day, 20-35N)
- Red Rock (short-day, 30-36N)
- Red Sensation (short-day, 25-35N)
- Texas Grano 1015Y (short-day, 25-35N)
- Vidora (short-day, 25-35N)
- White Castle (short-day, 30-38N)
Gabriella, Madalyn, Red Rock, and White Castle don’t have their own dedicated page on this site, but they’re worth knowing by name if you’re comparing seed catalogues.
Here’s the list that matters more, because it’s the one that explains a failed harvest. Every variety below is published for latitudes above Florida, meaning it’s a long-day or intermediate-day type that needs more daylight hours than this state’s sky ever provides. If a gardener has ever bought a supermarket onion set, or a bag labeled with a name like Walla Walla Sweet, and watched it grow tall, green, and healthy-looking all spring with no bulb ever swelling underneath, this is why.
- Ailsa Craig, Barolo, Blush, Bridger (long-day)
- Cabernet, Calibra, Candy, Elsye, Expression (intermediate-day)
- Frontier, Monastrell, New York Early, Patterson, Powell (long-day and intermediate-day)
- Red Carpet, Red Long of Florence, Red Long of Tropea, Redwing, Rossa di Milano (long-day and intermediate-day)
- Safrane, Scout, Sierra Blanca, Talon, Walla Walla Sweet (long-day and intermediate-day)
Plant any of these in Florida and the sequence is predictable: vigorous leaf growth all through fall and winter, since the plant is waiting for a daylight trigger that never comes, followed by the plant eventually bolting or simply declining as temperatures rise, and finally rot at the base as the bulb that should have formed never does. It isn’t a small or disappointing onion. It’s no onion at all.
When to plant onions in Florida
North Florida’s planting calendar follows the freeze dates, not a generic calendar month. NOAA’s 1991-2020 climate normals for the Jacksonville station put the last spring frost between February 16 and March 7, and the first fall frost between November 26 and December 13. Those are averages built from a 30-70% freeze probability band, not guarantees, and three of the thirty years in that data set saw no freeze at all at this inland airport site. Treat the window as a planning guide, not a promise.
For short-day onions in north Florida, that frost window points toward fall or late-winter planting rather than a spring start. Short-day varieties need to be in the ground early enough to build leaf growth during the cooler months, so that by the time daylight climbs toward that 13-hour-58-minute ceiling in spring, the plant has enough top growth to convert into a decent-sized bulb. Planting too late leaves a small plant trying to bulb on too little leaf mass, which usually means a small onion.
Central and south Florida run backward
This frost window belongs to Jacksonville and the surrounding panhandle-to-north-central stretch. Central and south Florida are effectively frost-free, and the growing calendar there flips: the productive season runs through the cooler winter months, and summer heat and humidity become the limiting factor instead of frost. A gardener in Orlando or Miami should not use these Jacksonville frost dates at all. Their onions go in during fall for a winter-into-spring harvest, following the same short-day daylight logic but on a calendar shifted by climate rather than frost risk.
Whichever part of the state you’re in, the frost dates are historical averages pulled from three decades of data, not a hard line drawn on a calendar. A cold snap can arrive outside that window, and a mild year can skip it entirely. Use the dates to plan a range, then watch your local forecast as the date approaches.
Sweet onions or onions that keep
Florida gardeners should plan on eating their onions, not storing them for months. That’s not a matter of variety choice so much as chemistry. According to University of Missouri Extension, sweet onions do not store as well as more pungent types, because the compounds responsible for pungency are volatile sulfur compounds, and those same compounds are what protect a bulb during long storage. Fewer of them makes for a milder onion on the cutting board and a shorter shelf life in the pantry.
Short-day onions, the only kind that reliably bulb at 30.48N, tend to run sweeter and milder for exactly this reason. That’s a fine trade for a Florida kitchen. These onions are meant to be used within weeks of harvest, not tucked away for a Thanksgiving dinner months later. Long-day onions, grown further north where daylight stretches past 14 hours in summer, build up more of those sulfur compounds and keep through winter into spring, which is why a onion bought at a Minnesota farm stand in October might still be firm in March while a Florida short-day onion from the same harvest would already be soft or sprouting.
The practical takeaway for a Florida pantry: plan your onion harvest as a rolling supply to use through spring and early summer, not a stockpile for the following winter. If long storage matters to your household, that’s a reason to pair fresh short-day onions from your own garden with pungent, long-keeping onions bought from a colder-climate source for the months when your own crop runs out. Trying to breed that trade-off away with a single variety isn’t realistic. It’s built into the same sulfur chemistry that gives a strong onion its bite in the first place.