Plant Library
How long is the growing season? US cities, 82–365 days
We measured the frost-free growing season for 1,025 US cities across all 50 states: it ranges from 82 days (Jackson, WY) to year-round (Miami, San Diego).
How long is the US growing season? 82–365 days by city
Hardiness zones tell you what survives your winter. But the number that actually governs your vegetable garden is the growing season — the frost-free stretch between the last spring frost and the first autumn frost. We pulled the average frost dates for 1,025 US cities (every state plus DC) from NOAA's 1991–2020 climate normals and measured that gap. The spread is enormous: a Wyoming gardener and a Florida gardener are not playing the same game.
Want your own city's dates? Look up your planting zone and frost dates by ZIP code, or browse the full open dataset of US frost dates by state.
The national range: 82 days to year-round
Across the 1,025 cities measured:
- Shortest: ~82 days
- Median: ~206 days
- Average: ~222 days
- Longest: 365 days (effectively frost-free)
That is a 4.5× difference between the shortest and longest mainland seasons — and 47 cities in the dataset are effectively frost-free (a year-round 365-day season). The practical meaning: a "start seeds 6 weeks before last frost" instruction lands in February for one reader and May for another.
Shortest growing seasons
The tightest seasons cluster in the Mountain West and the far north, where late-June frosts are normal:
| City | Growing season | Last spring frost |
|---|---|---|
| Jackson, WY | 82 days | June 15 |
| Bend, OR | 87 days | June 10 |
| Butte, MT | 91 days | June 8 |
| Fairbanks, AK | 92 days | May 25 |
In these places, fast-maturing crops and transplants (rather than direct sowing) are not optional — they are the only way to beat the frost.
Longest growing seasons
The longest seasons are in southern Florida, coastal California, and Hawaii — many with no reliable frost at all:
| City | Growing season |
|---|---|
| Miami & Key West, FL | 365 days |
| San Diego & Venice, CA | 365 days |
| Fort Lauderdale, FL | 365 days |
Here the limiting factor flips: instead of frost, it is summer heat and humidity that dictate the planting calendar.
By state: a 3× swing
Averaging each state's cities reveals the same gradient at the state level:
| Shortest-season states | Avg | Longest-season states | Avg |
|---|---|---|---|
| Wyoming | ~110 days | Hawaii | ~365 days |
| Alaska | ~116 days | Florida | ~320 days |
| Montana | ~123 days | California | ~314 days |
| Vermont / North Dakota | ~130 days | Arizona | ~276 days |
A Wyoming gardener gets roughly a third of the growing window a Florida gardener does — which is why "national" planting advice is almost always wrong for someone.
What this means for your garden
- Find your real dates. Use your USDA zone and frost dates by ZIP rather than a regional rule of thumb — local variability is real (±10 days even within a city).
- Match crops to your window. A 90-day season rules out long-season crops (many tomatoes, melons, winter squash) unless you start indoors and transplant.
- Time it from your last frost. Our planting calendar sequences sowing and transplanting around your zone's frost dates.
- Browse the data. The full per-state frost-date table is free to download on the US frost dates dataset.
Frequently asked questions
How long is the average US growing season?
Across the 1,025 US cities in our dataset (all 50 states plus DC), the median frost-free growing season is about 206 days and the average is about 222 days, based on NOAA 1991-2020 climate normals. Individual cities range from 82 days to a year-round 365.
Which US city has the shortest growing season?
Among the cities we measured, Jackson, Wyoming has the shortest at about 82 frost-free days, with a typical last spring frost around June 15. Bend (OR), Butte (MT) and Fairbanks (AK) are close behind, all under about 95 days.
Which places have a year-round growing season?
Effectively frost-free, 365-day seasons occur in southern Florida (Miami, Key West, Fort Lauderdale), coastal Southern California (San Diego, Venice) and Hawaii. In our dataset, 47 cities are effectively frost-free.
What is the difference between growing season and hardiness zone?
A USDA hardiness zone is based on the average annual minimum winter temperature and tells you what perennials survive your winter. The growing season is the frost-free gap between the last spring and first autumn frost — it tells you the window for planting and harvesting. They are related but answer different questions.
How do I find my growing season length?
Look up your last and first frost dates by ZIP code and subtract: the number of days between them is your growing season. Growli's ZIP zone lookup gives your USDA zone, average frost dates and growing-season length for any US ZIP.
Where does this frost-date data come from?
Frost dates are the averages from NOAA / NCEI 1991-2020 U.S. climate normals, mapped to 1,025 cities across all 50 states and DC, alongside their 2023 USDA hardiness zone. Real local variability is about plus or minus 10 days in a typical year.