Arkansas · zones 6b–8a
When to plant onions in Arkansas.
Sow or transplant between Jan 15 to Feb 28 in a typical year, keyed to Arkansas's median last frost around Mar 25. A second, fall sowing fits Sep 10 to Oct 22. Dates below are state medians; your ZIP code shifts them by days to weeks.
The 2026 windows
Onions dates for a typical Arkansas season.
1 · Start indoors
Dec 4 to Jan 17
About 6 weeks before set-out. Warm spot, real light.
2 · Set out
Jan 15 to Feb 28
Keyed to the ~Mar 25 last frost. Sow 0.5" deep, 4" apart.
Fall round
Sep 10 to Oct 22
Counted back from the ~Nov 5 first frost.
Harvest
~95 days later
~0.5 lb per plant over ~1 weeks.
Arkansas spans more than one climate: Zone 8 is the most common zone, but the state runs 6b to 8a. That's why the planner works from your ZIP code's frost dates, not your zone: mountain and coastal gardens in the same state can be three weeks apart.
Arkansas growing notes
South Arkansas can grow sweet onions the Ozarks cannot.
The state splits into two onion zones
Arkansas spans zone 6b in the Ozark highlands down to 8a along the Louisiana line, and that spread decides which onion category actually works where. Short-day onions trigger bulbing at about 10 to 12 hours of daylight and need a long, mild fall-to-spring stretch to build leaf mass first, and south Arkansas, averaging around 225 frost-free days a year statewide, delivers that reliably; the Ozark counties up north run several weeks shorter than the statewide figure and cannot support the same short-day strategy. North of the Arkansas River, that same variety runs out of cool growing weeks before it has built enough leaf, and the payoff is a small, disappointing bulb.
Texas Grano 1015Y and Yellow Granex, the Vidalia-type sweet onion, are proven short-day choices for southern Arkansas gardens, both capable of bulbs well over a pound in good ground and both mild enough to eat raw. Candy remains the dependable choice for gardeners north of the river, since it bulbs on a 12 to 14 hour trigger and does not depend on the long mild season the true short-day types need.
Delta humidity, not cold, is the real threat
Arkansas's Delta bottomland holds humidity long after sunrise, and downy mildew, showing as pale, fuzzy patches on the outer leaves during muggy mornings, is what actually threatens a south Arkansas onion crop rather than any late frost. Give transplants a full 4 inches of spacing so air can move between plants, and water at the base of the plant in early morning so foliage has hours to dry before the day heats up; leaves still wet at dusk are what let the spores take hold overnight.
Check the lower third of a few leaves weekly by holding them up to the light; a grayish-purple bloom visible through the leaf means downy mildew has started, and pulling that plant promptly protects the rest of the row better than any fungicide applied after the fact. Nitrogen split into 3 feedings through the leafy growth stage, rather than one heavy dose, keeps plants growing steadily without the soft, lush growth that disease moves through fastest.
Curing takes longer here than the seed packet says
Once tops fall over, cure bulbs somewhere shaded with real airflow, because Arkansas's Delta humidity slows the drying that curing depends on. A bulb neck should feel completely dry and papery when squeezed before it goes into storage; in a humid stretch that can take 3 to 4 weeks instead of the 2 weeks that works in a drier climate, and a box fan aimed across the drying rack cuts that time down materially while lowering the risk of mold setting into the necks.
Store finished bulbs at 35 to 40 degrees in mesh bags with airflow on all sides, never stacked in a closed container. A well-cured short-day sweet from south Arkansas typically holds 2 to 3 months before the sugar that makes it mild also makes it prone to softening, so plan to eat those first and save any pungent long-keepers from farther north in the state for later in the winter.
In Arkansas: watch for
The pests that find onions here.
A middle-length season, about 225 frost-free days, means onion, bulb overlaps onion thrips for a stretch each summer. Check plants every week or two and treat early.
Silvery streaks and curled leaf tips in hot spells.
Organic fix: Insecticidal soap or neem; hang sticky traps.
Seedlings wilt; white maggots in the bulb base.
Organic fix: Float a row cover over the row; rotate beds each year.
Pale patches with fuzzy gray growth in damp weather.
Organic fix: Space for airflow, water early in the day, spray neem.
White rot
Yellowing and dieback, then wilt; fluffy white mold at the bulb base and roots so rotted the plant lifts straight out.
Organic fix: No cure once it is in the soil. Plant clean stock, never follow onions with onions, and keep infested soil off tools and boots.
Your season math: Arkansas gives onions about 225 frost-free days, and it needs roughly 95 days to a first harvest. It's a one-planting crop, so time that single sowing well.
Planting onions in Arkansas: questions
When should I plant onions in Arkansas?+
In a typical Arkansas year, sow onions or set out transplants between Jan 15 to Feb 28, keyed to the state's median last frost around Mar 25. There's also a fall window: Sep 10 to Oct 22. Your exact dates shift with your ZIP code and microclimate.
When do I start onions seeds indoors in Arkansas?+
Start seeds inside about 6 weeks before set-out: roughly Dec 4 to Jan 17 for a typical Arkansas season.
What USDA zone is Arkansas?+
Arkansas spans zones 6b–8a, mostly zone 8. But frost dates, not zones, set planting time. The free planner uses your ZIP code's actual frost dates.
How many onions plants do I need?+
Depends who you're feeding. The crop page has exact counts per household size, or the free planner does the math for your family in about 60 seconds.