Growing Onions in Missouri: Which Varieties Actually Bulb

Missouri gardeners can absolutely grow onions, but only some varieties will actually form a bulb here. Plant the wrong one and you get a season of green leaves, a hard freeze, and a mushy nothing where a bulb should be. At 39.30 degrees north, near Kansas City, the reference station used for these figures sits at a latitude that puts most of Missouri in intermediate-day and long-day territory. Below, the varieties that match that latitude, the ones to avoid, the planting calendar, and what your onions will look like once they’re in the pantry.

How long your longest day is

Kansas City sits at 39.30 degrees north, and on the longest day of the year the sun is up for 14 hours and 46 minutes there. That single number decides almost everything about which onion varieties will bulb in a Missouri garden and which will not. Onions don’t respond to heat the way tomatoes or peppers do. They respond to day length. A short-day onion starts forming a bulb once daylight hits roughly 12 hours, according to Clemson Cooperative Extension’s Home & Garden Information Center. An intermediate-day type waits until closer to 12 to 14 hours. A long-day variety holds off until the day stretches to 14 or 16 hours before it switches from making leaves to making a bulb.

At 14 hours 46 minutes, Missouri clears the threshold for short-day onions early in the season, comfortably covers the intermediate-day range, and sits right at the low end of what long-day onions need. That’s the whole story in one sentence: this state can grow short-day, intermediate-day, and many long-day varieties, but it cannot grow the long-day types bred for the far north, because the day here simply never gets long enough for them.

Why the edges of the state matter

Missouri runs from around 36.5 degrees north near the Arkansas border to about 40.6 degrees north up by Iowa, a spread of roughly four degrees of latitude. That’s enough to shift the longest day by fifteen to twenty minutes from one end of the state to the other. A gardener in the Bootheel is a shade closer to short-day country. Someone farming near the Iowa line gets a bit more summer daylight than the Kansas City figure used here. Neither shift is dramatic enough to flip a variety from “will bulb” to “won’t,” but if you’re near either edge of the state, it’s worth checking your own latitude before you commit a full row to a variety that’s rated right at the boundary.

Which varieties bulb in Missouri

Of the 28 onion varieties documented on this site, 18 have a published latitude range that covers Missouri’s 39.30 degrees north. That’s the shortlist worth starting from:

• Ailsa Craig (long-day, 38-60N)
• Barolo (long-day, 38-55N)
• Blush (long-day, 38-55N)
• Bridger (long-day, 35-50N)
• Cabernet (intermediate-day, 35-45N)
• Calibra (intermediate-day, 35-45N)
• Candy (intermediate-day, 33-40N)
• Elsye (intermediate-day, 32-45N)
• Expression (intermediate-day, 32-45N)
• Monastrell (intermediate-day, 35-46N)
• New York Early (long-day, 38-50N)
• Patterson (long-day, 38-55N)
• Red Long of Florence (intermediate-day, 38-50N)
• Red Long of Tropea (intermediate-day, 35-48N)
• Rossa di Milano (long-day, 38-50N)
• Scout (intermediate-day, 32-46N)
• Sierra Blanca (intermediate-day, 32-45N)
• Walla Walla Sweet (long-day, 35-55N)

Three more sit close enough to a published boundary that they’re a genuine coin flip rather than a clean yes: Frontier (long-day, 40-50N), Red Carpet (long-day, 40-45N), and White Castle (short-day, 30-38N). These ranges are continuums, not hard cutoffs, so treat all three as “may bulb here” rather than a guarantee, and don’t plant your whole onion patch in any of them.

Now the part that matters more than the winners list. Seven varieties documented on this site have published ranges that simply don’t reach 39.30 degrees north, and planting them anyway follows a predictable, disappointing script.

• Gabriella (short-day, 20-35N)
• Madalyn (short-day, 20-35N)
• Red Rock (short-day, 30-36N)
• Powell (long-day, 43-47N)
• Redwing (long-day, 43-65N)
• Safrane (long-day, 42-50N)
• Talon (long-day, 42-50N)

The short-day varieties in that list fail in a specific way: they start bulbing while the plant is still small, because Missouri’s day length crosses their 12-hour trigger long before the plant has built up enough leaf mass to feed a decent bulb. You get onions the size of golf balls, sometimes marbles. The long-day varieties in that list fail differently, and worse. The day here never reaches the 14-to-16-hour window they’re bred for, so the plant never gets the signal to stop making leaves. It just keeps growing top growth all summer, and when frost arrives it hasn’t formed a bulb at all. What’s left in the ground rots. If you’ve ever bought a bag of supermarket sets, planted them, and ended up with tall green stalks and nothing underneath by fall, this is almost certainly why.

When to plant onions in Missouri

Planting dates follow day-length groups, and day-length groups follow latitude, which is why a planting calendar written for Georgia or Minnesota won’t line up with what works in Missouri. Here, the average last spring freeze runs from April 6 to April 20, and the average first fall freeze runs from October 18 to October 29, based on NOAA’s 1991-2020 climate normals for the reference station. Those are averages built on a 30 to 70 percent freeze probability band, not a promise. Treat them as a planning window, not a calendar date you circle in pen.

For the intermediate-day and long-day varieties that make up most of Missouri’s viable list, onion sets or transplants go in during late winter to early spring, timed so the plants have several weeks of cool growth before daylight climbs toward the bulbing threshold in early summer. That generally means getting plants in the ground four to six weeks ahead of the last frost window, which for most of Missouri lands sometime in late February through March, adjusted for how far north or south you garden in the state.

Missouri doesn’t have the mild winters that let Gulf Coast and Deep South gardeners get away with fall planting the way growers in Georgia or Louisiana do. An autumn-planted onion in Missouri risks a hard freeze killing young plants before they’ve built enough root system to survive winter, which is why spring planting is the standard approach here rather than the exception. If you’re gardening in the far southern edge of the state, near the Arkansas line, you have a bit more cushion than the Kansas City frost dates suggest, and some growers there push planting a week or two earlier. In the far north, near the Iowa border, add a similar buffer in the other direction and wait a little longer.

Sweet onions or onions that keep

Every onion gardener eventually runs into the same trade-off, and it isn’t about luck or variety marketing. It’s chemistry. According to University of Missouri Extension, “as a rule, ‘sweet’ onions do not store as well as the more pungent types.” The bite in a pungent onion comes from volatile sulfur compounds, and those same compounds are exactly what protects the bulb from rot during months in storage. A sweet variety has fewer of them. That makes it better sliced raw on a burger in July, and it also means it won’t make it to Thanksgiving in the cellar.

This lines up with day length, too. Short-day and many intermediate-day varieties, the kind favored in warmer, more southern growing zones, tend to run sweeter and milder, with a shorter shelf life. Long-day varieties, more common where summer daylight runs longer, tend to build more of those protective sulfur compounds and keep for months. Missouri sits in the middle of that spread, which means a Missouri garden can realistically produce both kinds, just not from the same plant.

What that means for your pantry: if you plant mostly intermediate-day sweet types like Candy or Elsye, expect onions that taste great in August and September but start softening and sprouting by December. If you lean toward long-day keepers like Patterson or Ailsa Craig, you trade a little sweetness for onions that hold firm in a cool, dark spot well into late winter, sometimes to March. A lot of Missouri gardeners split the difference and plant both, a shorter run of sweet onions to eat fresh through fall, and a longer-keeping batch braided or crated for the months when the garden itself is dormant.