Guide
Frost dates are the backbone of vegetable gardening, yet they're often misunderstood. Two numbers shape almost every planting decision you make: your last spring frost date and your first fall frost date. Together they define the window in which tender crops can grow safely outdoors. Here's what those dates actually mean and how to read them correctly.
A frost date is not a guarantee — it's a statistical average drawn from decades of historical weather records. The last spring frost date is the average date after which you're unlikely to see another freeze. The first fall frost date is the average date when freezing temperatures typically return. Most published frost dates, including the ones in the frost date planner, represent a 50% probability — meaning in half of all years, frost will still occur on or after that date.
Because a frost date is a midpoint, it carries real risk. If you transplant tomatoes exactly on your last frost date, there's roughly a coin-flip chance a later frost could still hit them. That's why many experienced gardeners add a buffer of one to two weeks past the listed date before setting out frost-sensitive crops like peppers, basil, and squash. Conservative timing costs you a little season length but protects against a single cold night wiping out weeks of work.
Climate agencies rarely calculate just one frost date — they derive a range of probabilities from the same 30-year record. Alongside the familiar 50% (median) date, you'll often see a 10% date (early in spring, when frost is still very likely to follow) and a 90% date (late, by which frost is nearly always finished). The National Weather Service defines the growing season itself as the span between the median last spring freeze and the median first fall freeze, so the standard published dates sit right in the middle of the risk curve. If you garden cautiously, plant tender crops closer to the 90% spring date; if you're willing to gamble a couple of weeks of extra season and keep row covers within reach, the 10–50% window is fair game.
Not all frosts are equal. The temperature at which damage occurs varies by plant:
| Type | Temperature | Effect |
|---|---|---|
| Light frost | 29–32°F | Damages tender plants |
| Moderate frost | 25–28°F | Damages most vegetables |
| Hard (killing) frost | Below 25°F | Kills most annuals |
A "frost" is measured as the air temperature roughly four feet above the ground dropping to 32°F or below. Ground-level temperatures on a clear, still night can be several degrees colder, which is why frost can settle in low spots even when the official reading stays above freezing.
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Because the spread between soil and air temperature drives so much of this, a simple soil thermometer is worth keeping in the garden — it tells you when the ground is actually warm enough to sow, which matters more than the calendar for cool-season crops.
The alerts your local forecast issues line up with those temperature bands. According to the National Weather Service, a Frost Advisory is issued when lows are expected to reach roughly 33–36°F on a clear, calm night during the growing season — conditions where frost can form even though the thermometer stays just above freezing. A Freeze Warning means temperatures are forecast to drop below 32°F for at least a couple of hours, enough to threaten unprotected tender crops. A hard freeze — generally below 28°F for a sustained stretch — kills most annual vegetables outright. When either appears in a spring or fall shoulder season, treat it as your cue to cover tender plants or hold off on transplanting.
The number of days between your last spring frost and first fall frost is your frost-free growing season. A short-season northern garden might have 90–120 frost-free days, while a mild southern climate can exceed 250. This number determines which crops will have time to mature — a melon that needs 100 days won't finish in a 90-day season without a head start indoors. To check any crop, compare its days-to-maturity (printed on the seed packet) against your frost-free window: if the two are close, start the seeds indoors, choose a faster variety, or extend the season with covers rather than gambling on an outdoor sowing.
Reliable frost dates are built from long-term climate records collected by agencies like NOAA's National Weather Service. Because they're averages, your own yard may run warmer or cooler depending on elevation, slope, and nearby structures — a phenomenon called microclimate. Treat published dates as a strong starting point, then adjust based on what you observe over several seasons.
Two gardens a mile apart can have frost dates a week or more apart. Cold air is denser than warm air, so on still nights it drains downhill and pools in low spots — a "frost pocket" at the bottom of a slope can freeze while a nearby rise stays clear. South-facing slopes and beds against a sunny wall warm faster and hold heat, buying a few extra frost-free days. Paved surfaces, buildings, and a large body of water nearby all moderate overnight lows. Track where frost lands first in your own yard over a couple of seasons; those notes often beat the published average for the specific bed you're planting. A min-max thermometer left in a problem bed logs each night's true low, so you can map your own frost pockets instead of guessing.
Can it frost above 32°F? Yes. Air temperature is measured about four to five feet up; on a clear, calm night the surface can be several degrees colder, so frost forms on leaves while the official reading shows 34–36°F.
Do frost dates change from year to year? The published averages shift only slowly as new climate data accumulates, but any single year can run early or late by two weeks or more — which is exactly why the dates are probabilities, not appointments.
Are the spring and fall dates equally reliable? Fall's first frost tends to be harder to predict than spring's last, because early-autumn cold snaps are more erratic. Give fall harvests a slightly wider safety margin.
Ready to find yours? The frost date planner gives your exact last and first frost dates plus a full planting schedule for 50+ crops.