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.
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.
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.
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.
Ready to find yours? The frost date planner gives your exact last and first frost dates plus a full planting schedule for 50+ crops.