Frost Dates Explained: Last and First Frost
Two dates govern your entire vegetable garden: the last spring frost and the first autumn frost. They mark the beginning and end of the frost-free growing season, and almost every sowing and transplanting decision is calculated from them. Here is what the dates mean, where to find yours, and how to use them with confidence.
Your last spring frost date is the 30-year average date of the final 32°F freeze of spring; your first autumn frost date is the 30-year average date of the first 32°F freeze of autumn. The days between them form your growing season — about 120–150 days in cold climates and 200+ where winters are mild. Count backwards from the last frost to start seeds indoors, set tender transplants out 1–2 weeks after it (nights above 50°F, soil at least 60°F), and count backwards from the first autumn frost to time fall sowings.
What a frost date actually means
A frost date is not a forecast. It is a statistic: the average date, over the standard 30-year climate record (currently 1991–2020), on which the temperature last fell to 32°F in spring, or first fell to 32°F in autumn, at the nearest official weather station. In roughly half of all years the real frost lands before the date, and in half it lands after — which is why experienced gardeners treat it as the middle of a window, not a promise.
Two practical notes. First, 32°F is measured in a ventilated shelter about 5 feet above the ground. On a clear, still night the air at leaf level can run several degrees colder, so tender foliage can frost even when the official low stays just above freezing. Second, “last frost” always means spring and “first frost” always means autumn — each year has one of each, and together they define the frost-free growing season.
Frost vs freeze: the temperature ladder
Not all cold nights are equal. Extension services use this ladder, and it is worth learning because each rung demands a different response:
| Reading | Name | What it does to plants |
|---|---|---|
| 36°F and below at plant level | Light frost | Tender crops such as basil, tomatoes and peppers show leaf damage; hardy crops unaffected |
| 32°F | Freezing point | Water in plant cells can freeze; tender annuals damaged |
| 28°F | Hard freeze | Most warm-season annuals killed outright |
| 25°F and below | Killing freeze | Damages even hardy annuals; ends the season for unprotected crops |
Gardeners generally plan tender crops around 32°F and treat 28°F as the practical end of the season. A simple fabric row cover typically buys 2–6°F of protection — often the difference between a light frost and a lost planting.
Typical frost dates across the US
Typical 30-year averages, rounded to the nearest five days. Your ZIP code can easily differ by one to two weeks depending on elevation, nearby water and urban heat:
| City | Last spring frost | First autumn frost | Frost-free season |
|---|---|---|---|
| Minneapolis, MN | 10 May | 1 Oct | ~145 days |
| Denver, CO | 5 May | 5 Oct | ~153 days |
| Chicago, IL | 20 Apr | 25 Oct | ~188 days |
| New York, NY | 15 Apr | 10 Nov | ~210 days |
| Seattle, WA | 15 Mar | 15 Nov | ~245 days |
| Atlanta, GA | 20 Mar | 10 Nov | ~235 days |
| Dallas, TX | 15 Mar | 20 Nov | ~250 days |
| Los Angeles, CA | 30 Jan | 10 Dec | ~315 days |
Finding your dates for your ZIP code
- Your state extension service. Most publish frost-date tables by county or weather station — search “[your state] extension frost dates”. This is the most trustworthy source.
- NOAA and National Weather Service climate pages. These publish the underlying 30-year normals for thousands of stations.
- Almanac-style ZIP-code tools. Quick and convenient for a first estimate, but confirm against your extension’s table, which uses the stations nearest you.
Use the station closest to you with similar elevation. A station 500 feet higher up, or 20 miles further inland, can easily run a week later in spring.
The 50% date vs the 90% date
Good frost tables list several dates for the same place: the dates by which there is a 50%, 70% or 90% chance the frost-free season has begun. The 50% date is the plain average — a coin flip. The 90% date is the cautious gardener’s date: in only one year in ten does frost strike after it.
Rule of thumb: start cool-season crops around the 50% date, and hold tender transplants until the 90% date has passed. In most of the US the two dates sit 2–3 weeks apart.
Putting frost dates to work
Nearly every entry on the gardening calendar is an offset from one of the two dates:
| Garden task | Timing rule |
|---|---|
| Start tomatoes and peppers indoors | 6–8 weeks before the last frost |
| Start brassicas (cabbage, broccoli) indoors | 4–6 weeks before the last frost |
| Sow peas, spinach and broad beans outdoors | 4–6 weeks before the last frost (soil 40°F+) |
| Transplant tomatoes outdoors | 1–2 weeks after the last frost; nights above 50°F, soil 60°F+ |
| Transplant peppers and eggplant | 2–3 weeks after the last frost; nights above 55°F, soil 65°F+ |
| Direct-sow beans, corn and squash | After the last frost; soil 60°F+ |
| Sow autumn carrots and beets | 10–12 weeks before the first autumn frost |
| Sow autumn radish and lettuce | 4–6 weeks before the first autumn frost |
Two worked examples. If your last frost is 15 April: start tomatoes indoors around 18 February to 4 March (6–8 weeks before), and transplant around 22–29 April. If your first autumn frost is 15 October: sow autumn carrots between 21 July and 4 August (10–12 weeks before).
Get your seed-starting dates right
The Seed Starting Calendar Generator (coming soon) turns your ZIP code into a printable sowing schedule for every crop in this guide.
Microclimates: your garden is not the weather station
- Cold air flows downhill and ponds in low spots — the bottom of a slope can frost a full week before the top.
- Walls, fences and the house radiate stored heat. Beds against a south-facing wall gain several frost-free days at each end of the season.
- Raised beds warm earlier in spring (good for early sowing) but also freeze sooner in autumn — plan accordingly.
- Urban gardens run a few degrees warmer than the surrounding countryside thanks to the heat-island effect.
- A soil thermometer beats the calendar. Seeds and transplants respond to soil temperature, not dates — measure before you sow.
Frequently asked questions
Is the last frost date a guarantee?
No. The headline date is the 50% probability date — roughly a coin flip. About half the time the real last frost falls later. If a late frost would ruin expensive transplants, wait for the 90% frost-free date instead, or keep row cover handy.
Frost is forecast after I already transplanted. What now?
Cover tender plants with fabric row cover, upturned buckets or cardboard boxes before nightfall, and water the soil in the late afternoon — moist soil holds more heat. Uncover in the morning so plants do not overheat. One covered night at 30°F is survivable; an uncovered one often is not.
Do frost dates change over time?
Yes. The 30-year normals are recalculated every decade, and the long-term trend across most of the US is toward earlier last frosts and later first frosts — a lengthening season. Check your dates every few years rather than relying on a remembered figure.
What is the difference between a frost date and a hardiness zone?
A hardiness zone describes the average coldest winter night — it tells you which perennial plants survive winter. Frost dates describe the length of the frost-free season — they tell you which annual vegetables can mature in a year. You need both numbers.
Can I plant before the last frost date?
Cool-season crops, yes: peas, spinach, broad beans and onions tolerate light frosts, provided the soil has reached about 40°F. Warm-season transplants — tomatoes, peppers, eggplant, basil — should wait until 1–3 weeks after the date, with warm nights and warm soil.
Related guides
How to Grow Tomatoes in a Raised Bed
Transplant timing around the last frost is half of tomato success — spacing, soil and feeding are the other half.
Easiest Vegetables to Grow for Beginners
Ten forgiving crops with cool-season options for short seasons and warm-season stars for long ones.
How Often Should I Water My Vegetable Garden?
Watering numbers for every stage of the growing season, from seedling to harvest.
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