Tennessee · zones 7a–8a
When to plant onions in Tennessee.
Sow or transplant between Jan 29 to Mar 14 in a typical year, keyed to Tennessee's median last frost around Apr 8. A second, fall sowing fits Aug 30 to Oct 11. Dates below are state medians; your ZIP code shifts them by days to weeks.
The 2026 windows
Onions dates for a typical Tennessee season.
1 · Start indoors
Dec 18 to Jan 31
About 6 weeks before set-out. Warm spot, real light.
2 · Set out
Jan 29 to Mar 14
Keyed to the ~Apr 8 last frost. Sow 0.5" deep, 4" apart.
Fall round
Aug 30 to Oct 11
Counted back from the ~Oct 25 first frost.
Harvest
~95 days later
~0.5 lb per plant over ~1 weeks.
Tennessee spans more than one climate: Zone 7 is the most common zone, but the state runs 7a 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.
Tennessee growing notes
Tennessee sits right on the line between two onion day-length worlds.
Latitude decides which bag of sets to buy
Tennessee spans roughly 35 to 36.5 degrees north, which puts the whole state inside the intermediate-day band: varieties that trigger bulbing once daylight reaches 12 to 14 hours, rather than the short-day types sold for the Deep South or the long-day types bred for the northern states. Candy and Super Star both fit that band well and are the safer picks off a Tennessee seed rack. A long-day onion here never sees the 14 hours it waits for, so it spends the season making tops and hands you a thick neck instead of a bulb. A short-day type has the opposite problem: it flips into bulbing in early spring, before it has built the leaves to fill one, and stays small.
Onion transplants take frost without flinching, so set them out two to four weeks before your last frost date, not after it: every week you wait costs a leaf, and every leaf is a ring in the finished bulb. Keep nitrogen coming while that leaf growth is still underway, then back off once the base of the plant visibly starts to swell, because from that point forward the plant is spending stored leaf growth on the bulb rather than adding anything new.
Curing fights the same humidity as everything else
A Tennessee fall rarely offers the bone-dry air that makes curing easy in a desert climate; instead it offers warm, sticky stretches that keep bulbs from drying down cleanly if they are left in a pile or a closed bag. Spread pulled bulbs in a single layer somewhere shaded with real airflow, a covered porch, an open garage with a box fan running, or a mesh rack, rather than piling them in a basket where the center never dries.
Forget the calendar and judge doneness by feel: give the neck a gentle squeeze around the two-week mark, and if it still gives like a green stem, it needs more days on the rack; once it resists like a dry twig about to snap, the bulb has finished. Move cured bulbs into a cool, airy spot for storage, because Tennessee's lingering fall humidity will soften anything left in a closed container, while loose mesh bags that let air pass through keep that softening from happening.
Maggot in a wet spring, thrips in a dry summer
A cool, wet Tennessee spring is exactly when seedcorn maggot moves in, chewing its way into a young transplant's base until the leaves collapse and the whole plant lifts free on rotted, mushy roots with almost no resistance. The fly is drawn hardest to a bed freshly turned with green manure or heavy undecomposed compost, so let organic matter break down for a few weeks before setting transplants into it. Cover transplants with floating row cover the day they go in the ground so the adult fly has nowhere to lay its eggs, and skip planting onions or garlic in any bed that grew either crop within the past three years, which starves out the local population before it can build back up.
Thrips move in once summer turns hot and dry, leaving thin silvery scratches along the leaf blades where they have been feeding. Hold a leaf up to early morning light and look for those pale streaks, or check down in the leaf axils with a hand lens for the insects themselves, slivers no longer than a grain of rice. A leaf showing several scratches is your cue to treat with insecticidal soap, worked into the crease where the leaves meet the neck since that is where thrips tuck out of a direct spray.
In Tennessee: watch for
The pests that find onions here.
A middle-length season, about 200 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: Tennessee gives onions about 200 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 Tennessee: questions
When should I plant onions in Tennessee?+
In a typical Tennessee year, sow onions or set out transplants between Jan 29 to Mar 14, keyed to the state's median last frost around Apr 8. There's also a fall window: Aug 30 to Oct 11. Your exact dates shift with your ZIP code and microclimate.
When do I start onions seeds indoors in Tennessee?+
Start seeds inside about 6 weeks before set-out: roughly Dec 18 to Jan 31 for a typical Tennessee season.
What USDA zone is Tennessee?+
Tennessee spans zones 7a–8a, mostly zone 7. 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.