When to plant · 22 cities · zones 7b–8a
When to plant onions in Tennessee
Start Spanish Onion seeds indoors around Jan 12 and transplant around Mar 9 — the Tennessee statewide median, counted from a last spring frost of Apr 6 across 636 ZIP codes and 154 NOAA stations.
The rule: Twelve weeks indoors, the earliest sowing on the calendar, then transplant about four weeks before the last frost.
13 of these Tennessee cities sit below 36° N, where a long-day onion never gets the day length to bulb. They are flagged in the table; plant a short-day type there.
Tennessee onions, by step
Statewide median last frost Apr 6, first fall frost Oct 29, 2027 season. Each cultivar's own indoor lead time and days to maturity, same engine as the Plan Builder.
| Cultivar | Start indoors | Plant out | First harvest | Days |
|---|---|---|---|---|
| Spanish OnionYellow Sweet Spanish (long-day) | Jan 12 | Mar 9 | Jun 27 | 110 from transplant |
Tight means first harvest lands within two weeks of the median first fall frost. Statewide dates are the ZIP-weighted median of every NOAA 1991–2020 station Tennessee's ZIP codes resolve to.
Onions in Tennessee, city by city
Spanish Onion, scheduled from each city's nearest NOAA station — the same dates as its frost page.
| City | Last frost | Start indoors | Plant out | First harvest |
|---|---|---|---|---|
| Nashvillezone 7b | Apr 1 | Jan 7 | Mar 4 | Jun 22 |
| Memphiszone 8abelow 36° N · short-day onion | Mar 16 | Dec 22 | Feb 16 | Jun 6 |
| Knoxvillezone 7bbelow 36° N · short-day onion | Apr 11 | Jan 17 | Mar 14 | Jul 2 |
| Chattanoogazone 8abelow 36° N · short-day onion | Mar 24 | Dec 30 | Feb 24 | Jun 14 |
| Clarksvillezone 7b | Apr 10 | Jan 16 | Mar 13 | Jul 1 |
| Murfreesborozone 7bbelow 36° N · short-day onion | Apr 9 | Jan 15 | Mar 12 | Jun 30 |
| Franklinzone 7bbelow 36° N · short-day onion | Apr 15 | Jan 21 | Mar 18 | Jul 6 |
| Johnson Cityzone 7b | Apr 19 | Jan 25 | Mar 22 | Jul 10 |
| Jacksonzone 7bbelow 36° N · short-day onion | Apr 2 | Jan 8 | Mar 5 | Jun 23 |
| Hendersonvillezone 7b | Apr 11 | Jan 17 | Mar 14 | Jul 2 |
| Smyrnazone 7bbelow 36° N · short-day onion | Apr 13 | Jan 19 | Mar 16 | Jul 4 |
| Spring Hillzone 7bbelow 36° N · short-day onion | Apr 3 | Jan 9 | Mar 6 | Jun 24 |
| Kingsportzone 7b | Apr 9 | Jan 15 | Mar 12 | Jun 30 |
| Bartlettzone 8abelow 36° N · short-day onion | Mar 29 | Jan 4 | Mar 1 | Jun 19 |
| Gallatinzone 7b | Apr 16 | Jan 22 | Mar 19 | Jul 7 |
| Colliervillezone 8abelow 36° N · short-day onion | Mar 29 | Jan 4 | Mar 1 | Jun 19 |
| Lebanonzone 7b | Apr 10 | Jan 16 | Mar 13 | Jul 1 |
| Clevelandzone 7bbelow 36° N · short-day onion | Apr 6 | Jan 12 | Mar 9 | Jun 27 |
| Columbiazone 7bbelow 36° N · short-day onion | Apr 10 | Jan 16 | Mar 13 | Jul 1 |
| Brentwoodzone 7bbelow 36° N · short-day onion | Apr 15 | Jan 21 | Mar 18 | Jul 6 |
| Mount Julietzone 7b | Apr 1 | Jan 7 | Mar 4 | Jun 22 |
| La Vergnezone 7b | Apr 13 | Jan 19 | Mar 16 | Jul 4 |
What these onions become
What Tennessee onions need
Yellow Sweet Spanish Onion Seed
A long-day storage onion with enough sugar to sweat down without scorching. The aromatic base under every tomato sauce on this site.
Organic Seed Starter Potting MixMust have
Seed-starting mix is not potting soil with a nicer label — it is finer, lighter, and low in nutrients on purpose, because a seedling's first roots want air and moisture, not fertiliser.
72-Cell Trays with 1020 Bottoms, 5-PackMust have
The cheap black nursery trays crack after one season and flex enough to break roots when you lift them. These do not. Over five seasons the price per use is lower than the throwaways.
T8 Full-Spectrum Grow Lights, 1 ft 4-packMust have
A south window in March delivers a fraction of the light a pepper seedling needs, and the plant tells you by stretching. Two inches of LED above the canopy for 16 hours a day fixes it permanently.
Rapitest Soil Test Kit
In-ground growers are guessing until they test. pH outside 6.0–6.8 locks nutrients out no matter how much fertiliser you add, and no amount of feeding fixes that.
Pure Organic Worm Castings, 15 lb
Not a fertiliser so much as a soil-biology inoculant with a mild nutrient charge. A cup in each planting hole is a cheap, unglamorous improvement you can measure by August.
Garden Harvest Basket with Tool Caddy
A harvest basket that doubles as a colander means the hose rinse happens in the garden, and the dirt stays outside. On a 20-pound tomato day that is a genuine time saving.
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Onions in Tennessee: questions
When should I plant onions in Tennessee?
Transplant around Mar 9 at the statewide median; across the state that date runs from Feb 28 in the warmest tenth of Tennessee's ZIP codes to Mar 23 in the coldest. To cut the freeze risk to one year in ten, count from Apr 23 instead of the median last frost. Use the city table for your own town.
When do I start onions seeds indoors in Tennessee?
Around Jan 12 for Spanish Onion: 12 weeks before the statewide median last frost, on soil held at 65–75 °F.
When is the last frost in Tennessee?
The ZIP-weighted median of NOAA 1991–2020 station medians is Apr 6. In the warmest tenth of Tennessee's ZIP codes the median last frost falls on or before Mar 28; in the coldest tenth, on or after Apr 20.
When will Tennessee onions be ready to harvest?
Spanish Onion planted on the statewide date is ready around Jun 27: 110 days from transplant.
Which onions grow in Tennessee?
Spanish Onion is a long-day onion: it bulbs at 14–16 hours of daylight, which it gets above roughly 36° N. 13 of the 22 Tennessee cities listed here sit below that line; grow a short-day onion there.
More for Tennessee
- When to plant tomatoes
- When to plant peppers
- When to plant tomatillos
- When to plant basil
- When to plant cilantro
- When to plant carrots
- When to plant mustard greens
Onions in every state → · Tennessee frost dates → · How frost-date math works →