Find Your Frost Dates by ZIP Code: A Planting Guide

Frost dates are historical risk estimates, not promises about this year’s weather. Enter your ZIP code in the planner to see your typical spring and autumn freeze windows — then check the temperature threshold and the probability behind each date. Use those windows together with your crop’s cold tolerance, your soil temperature, and the current forecast. The planner’s heat summary can also help you steer transplanting away from your hottest stretch.

Sophie was sitting on the wooden garden bench in the afternoon sun, totally puzzled, flipping through dog-eared seed catalogs and weather apps. “When’s my frost again? And what am I supposed to plant when?”

Sprouty hopped up onto the bench right beside her with a grin: “Stop guessing! Your frost date isn’t an appointment — it’s a risk estimate. Pop your ZIP code into the Frost & Heat Planner and it’ll show you the odds, not just a date.”

First, Open the Planner and Read Its Labels

Before you trust any frost date — from our planner or anyone else’s — confirm four things:

1. The dataset. Our planner is built on the NOAA 1991–2020 U.S. Climate Normals: 30 years of weather-station records. A date built on a different period, a single backyard thermometer, or an unknown source isn’t the same thing.
2. The temperature threshold. Our freeze dates use 32°F. A date built on a 36°F “frost” threshold or a 28°F hard-freeze threshold answers a different question.
3. What the probability means. A 10% spring date and a 10% fall date mean opposite things (the tables below spell this out). Not every product labels them the same way — check before you compare dates across sources.
4. What it shows where freezes are rare. Parts of Florida don’t freeze every year, and the Florida Keys have never recorded freezing temperatures (NOAA). If that’s your climate, look at what the tool shows instead of a date — don’t force a number where nature didn’t provide one.

The Big Gardening Myth: “My USDA Hardiness Zone Tells Me When to Plant”

The single most widespread misconception in home gardening is using your USDA Plant Hardiness Zone to schedule seed starting and planting dates.

As explained by the USDA Agricultural Research Service, your hardiness zone is calculated exclusively from the average annual extreme minimum winter temperature over a 30-year span, in 10°F bands. That winter minimum is invaluable for knowing whether a perennial shrub, fruit tree, or rose can survive midwinter — it tells you nothing about when spring begins or when autumn ends. (Zones themselves do shift over time — see what the updated hardiness zones mean for what you grow.)

• Coastal Pacific Northwest (Zone 8b): mild maritime winters, but cool damp spring soils linger well into May and autumn freezes may wait until mid-to-late November.
• Central Texas (Zone 8b): the exact same zone rating — yet last spring frosts can wrap up by mid-March while blistering summer heat arrives by June.
• Piedmont North Carolina (Zone 8a): similar winter minimums, but completely different rainfall patterns, late spring cold snaps, and October frost windows.

If gardeners in Seattle, Austin, and Raleigh all planted tomatoes on the same day because they share a zone, most would watch seedlings rot in chilly mud or die in a snap frost. To schedule planting, you need historical freeze probabilities and local climate normals — not just winter extremes.

Spring and Fall Ask Two Different Probability Questions

Here’s the part most articles mangle. A spring percentage and a fall percentage do not mean the same thing:

• Spring: the probability that the last freeze falls later than the date shown.
• Fall: the probability that the first freeze falls earlier than the date shown.

That’s why a single combined table gets confusing. Read them separately:

Last spring freeze (32°F)

Planner date	What it means	How gardeners use it
90%	In 9 of 10 years, the last spring freeze falls after this date.	The earliest date in the set — only peas, spinach, and the hardiest crops go out now.
50% (median)	In about 5 of 10 years, the last freeze falls after this date.	The commonly published date — but confirm which probability your source used. It’s a coin flip for tender crops.
10%	In only 1 of 10 years does a freeze fall after this date.	The most conservative transplant date in the table for tomatoes, peppers, and basil — still roughly a 1-in-10 risk, so check the forecast before planting out.

First fall freeze (32°F)

Planner date	What it means	How gardeners use it
10% (earliest)	In only 1 of 10 years does the first fall freeze arrive before this date.	Early-warning date — start watching forecasts and have row cover ready. (NOAA’s “Earliest 10%” map.)
50% (median)	In about 5 of 10 years, the first freeze arrives by this date.	Mid-range planning date for fall harvest math.
90% (latest)	In 9 of 10 years, the first freeze has already arrived by this date.	Late date — tender harvests should be finished well before this. (NOAA’s “Latest 10%” map.)

These tables follow NOAA’s standard convention. If another source words its probabilities differently, translate before comparing dates. (NOAA NCEI: when to expect the first fall freeze)

Frost, Freeze, and Hard Freeze: Which Number Are You Reading?

Gardeners use “frost date” loosely, but the planner’s dates are freeze dates — and the distinction matters:

• Freeze (32°F / 0°C): the threshold behind every date in the tables above. Tender crops like basil, tomatoes, and peppers are damaged at or near this temperature.
• Hard freeze (28°F / −2°C and below): kills most tender vegetation outright and ends the season for warm-season crops. Even hardy greens take damage here.
• Frost on the leaves: the white crystals can form on plant surfaces when the air temperature reads a few degrees above 32°F — leaves radiate heat straight to a clear night sky and cool below the air around them. That’s why a forecast low of 36°F can still frost your peppers (more on this in the microclimate section below).

Worked Example: Counting Backward for a Fall Harvest

Say the planner shows your 50% first fall freeze around October 20 — a hypothetical date to show the math. You want fall carrots, and the packet says 70 days to maturity:

1. Start from the freeze date: October 20.
2. Count back the days to maturity: 70 days lands around August 11.
3. Add a buffer for slowing autumn growth. Many gardeners add a rough 1–2 week buffer for the “Persephone period” — when daylight drops below about 10 hours and growth slows to a crawl. Treat it as a rule of thumb, not a constant: the slowdown bites harder at higher latitudes, and leafy greens stall more than root crops. So you’d aim for early August, not August 11 on the dot.

One critical detail: check what the packet’s “days to maturity” counts from. For direct-sown crops (carrots, beans, radishes) it’s days from sowing. For crops you start indoors (broccoli, cabbage, cauliflower), it’s usually days from transplanting — so count back to your transplant date first, then count back the indoor growing time on the packet to find your sow date. (New to indoor sowing? See our guide to starting seeds indoors.)

And remember: a historical date is a planning input, not a forecast. When the real week arrives, check the actual 7–10 day forecast and be ready to cover.

Why Your Backyard Frosts Before the Weather App Says So

Checked your phone on an October morning, saw a forecast low of 36°F, and walked out to frosted pepper leaves? You aren’t imagining it. Three things explain the gap, as detailed by the National Weather Service:

1. Measurement height vs. ground level: official thermometers sit in ventilated shelters 5 to 6 feet up. On clear, windless nights, dense cold air sinks — soil and leaf temperatures can run 3°F to 6°F colder than the official reading at shoulder height.
2. Radiational cooling: under a clear sky, leaves radiate heat straight out as infrared energy and cool faster than the surrounding air. Leaf tissue at 32°F freezes even when the air measures 35°F or 36°F.
3. Cold-air drainage: cold air flows downhill like water and pools in low spots and against solid fences. A garden at the bottom of a slope can freeze a week or two earlier in fall — and later in spring — than one on a ridge.

The Other Half of the Season: Midsummer Heat

Most planting guides obsess over frost. But in many regions, extreme heat does as much damage as a freeze — it just doesn’t get the same attention.

When days spike above 90°F and nights stay warm, tomato and pepper blossoms can drop without setting fruit: heat can reduce pollen viability, stalling your harvest for weeks. How much damage occurs depends on the variety, humidity, and how long the heat lasts — it isn’t a single uniform threshold (University of Maryland Extension). Heat also pushes cool-season greens like spinach, lettuce, and cilantro to bolt — flowering early, turning bitter, and stopping leaf production.

That’s why the planner includes a monthly Heat Watch: the average number of days per month your area tops 90°F, from NOAA 1991–2020 Normals. Treat it as a planning signal, not a doom forecast — it tells you when to get warm-season crops in early enough to set fruit before the scorch, and when to hold fall sowings until temperatures break. Then pair it with the current season’s forecast, the same way you would a frost date.

Connecting the Dots: Use Your Dates Around the Garden

Pairing with the planting calendar: use your frost window alongside our interactive Vegetable Planting Calendar for indoor start dates, direct sow dates, and transplant targets customized for your region.

Knowing what to plant right now: unsure whether to start cool-season seeds or wrap up summer beds? What to Plant Now shows immediate recommendations based on today’s date and your local frost schedule. And if frost caught you off guard, see why sweet potatoes must come out the day frost strikes.

Looking for more seasonal guidance? Read our comprehensive Seasonal Tips Playbook, learn the secret to timing cool-weather greens in our late September spinach seeding guide, and explore all of our free garden tools starting with Sprouty’s Frost & Heat Planner.