First frost date
what it means and how to find yours

How frost date estimates are made: climate normals and probabilities

In the United States, the most authoritative source is the U.S. Climate Normals produced by NOAA’s National Centers for Environmental Information (NCEI). Climate normals summarise conditions at thousands of weather stations over a long period; NCEI describes its conventional normals as 30-year normals, with the current release covering 1991–2020. Alongside temperature and precipitation, NCEI lists frost and freeze dates among the normals variables it publishes. See the NCEI U.S. Climate Normals product page.

Because the first autumn freeze arrives on a different date each year, frost information is best understood as a probability. Instead of one date, a full frost-freeze summary shows how the chance of a freeze having occurred rises through the autumn, and may give dates for more than one temperature threshold. A single “average” or median date is the middle of that range, which means that in many years frost arrives before it. Cautious gardeners plan around an earlier, lower-risk date for valuable tender plants and treat the average as a rough midpoint.

Two more points help when reading any estimate. First, normals describe the past period they were calculated from, and a changing climate can shift what recent autumns look like compared with those averages. Second, a station may sit in a city, an airport or a valley that does not match your garden. That is why local knowledge and your own measurements, covered below, are worth so much.

How to look up your local first frost estimate

We deliberately do not publish a table of dates by city or state on this page. Such tables go out of date, hide the probability behind a single number and often come from a station far from your garden. Instead, go to the sources below and pick the station closest to you in distance, elevation and surroundings.

• NOAA NCEI U.S. Climate Normals. The NCEI U.S. Climate Normals Quick Access tool lets you search for a station and view its normals. Look for the frost/freeze or agricultural normals, note which temperature threshold and probability each figure refers to, and compare a couple of nearby stations if you can.
• Your local National Weather Service office. The National Weather Service provides the actual forecasts and issues frost and freeze alerts for your area. Many local offices also publish climate summaries and growing-season information for their region. Climate normals tell you when frost usually comes; the NWS forecast tells you whether it is coming this week.
• Cooperative Extension. Every U.S. state has a Cooperative Extension service connected with its land-grant university, and extension offices publish frost dates, planting calendars and plant-protection advice tuned to local conditions. Search for your state’s extension service or county office by name. The Extension Foundation is a national partner organisation to Cooperative Extension and a starting point for finding extension resources.
• Local gardeners and records. Master gardener groups, garden clubs, nurseries and long-time neighbours often know which parts of town frost first. Their observations complement the official numbers.

A common mix-up is worth flagging. The USDA Plant Hardiness Zone Map is based on the average annual extreme minimum winter temperature. It tells you which perennials are likely to survive your winters, not when your first autumn frost arrives. Two places in the same hardiness zone can have quite different frost dates, so use the zone map for choosing plants and the frost data for timing.

Frost vs freeze: what is the difference?

The two words are often used interchangeably, but they describe different things.

• Frost is ice crystals that form on surfaces, such as leaves, grass, car roofs and fences, when those surfaces cool to freezing and moisture from the air deposits as ice. Because exposed surfaces radiate heat on clear nights, they can get colder than the air at the height where thermometers usually measure. That is why you can see frost on the lawn even when the reported air temperature stayed a little above freezing.
• Freeze refers to the air temperature itself falling to or below freezing. The National Weather Service explains that a freeze occurs when the temperature drops below 32°F; see its cold weather safety page. A freeze can damage plants whether or not visible frost forms, for example on a windy or dry night when no ice crystals appear.
• Frost advisories and freeze warnings. National Weather Service offices issue frost and freeze alerts, particularly around the start and end of the growing season. Criteria vary by region and season, so read the alert text for your area and treat it as a cue to protect plants and pipes.

For gardeners, the difference matters because a light frost on a calm night may only damage the most tender leaves, while a longer, harder freeze can kill tender plants outright and damage exposed water lines. How cold, for how long and how protected a plant is all affect the outcome.

Track frost in your own yard with a thermometer or weather station

Official frost dates describe a weather station; your plants live in your yard. A modest thermometer setup turns guesswork into your own local record and gives you a warning on the nights that matter.

• Min/max memory. A thermometer that records the overnight minimum tells you how cold it actually got while you slept. Check it each morning in autumn and you quickly learn how your garden compares with the forecast. Most outdoor thermometers with a digital display offer this.
• Low-temperature alerts. A Wi‑Fi thermometer or a station app can send an alert to your phone when the temperature falls below a level you choose, so you can cover plants or bring pots in before it is too late. Set the alert a few degrees above freezing to give yourself time, because surfaces can frost before the air at sensor height reaches freezing.
• History and graphs. A Wi‑Fi weather station with app history, or a data-logging Wi‑Fi sensor, builds a season-by-season record. After a few autumns you will know whether your first frost tends to run earlier or later than the official estimate.
• More than one sensor. If your garden has a frost pocket, a greenhouse or a vegetable bed far from the house, an extra sensor there shows the difference. Many wireless weather stations and gateway thermometer systems accept several remote sensors.
• Sensor height and placement. Standard air temperature is measured above the ground in a shaded, ventilated shield. A sensor at that height gives readings comparable with official data; a second sensor near plant height or close to the ground shows the colder air your seedlings actually feel. Keep sensors out of direct sun and away from walls and paving, which store heat, as explained in the outdoor thermometer guide.
• Humidity and dew point. Stations and combined sensors that report humidity or dew point give extra context for frost risk on clear nights. The thermo-hygrometer section of our hygrometer guide explains combined units.

Use your own readings alongside the forecast, not instead of it. If the National Weather Service issues a frost or freeze alert for your area, act on it even if your own sensor has not dropped yet.

Protecting plants on a frost night

• Cover in the late afternoon or evening, before the temperature drops, to trap heat that the ground stored during the day.
• Let covers reach the ground. Drape frost cloth or sheets over plants and down to the soil, and secure the edges. A cover that only sits on top lets ground heat escape out of the sides.
• Keep plastic off the leaves. Plastic touching foliage can conduct cold to the leaves. If you use plastic, support it on a frame so it does not touch the plants.
• Remove covers in the morning once temperatures rise, so plants get light and do not overheat under the cover.
• Bring containers indoors or move them against a sheltered wall. Pots lose heat faster than plants in the ground.
• Water if the soil is dry. Many extension services advise watering dry soil ahead of a frost because moist soil can hold and release more heat than dry soil. Avoid soaking plants in the evening.
• Use cold frames, cloches or row covers for beds you want to extend into autumn.
• After a frost, wait before pruning damaged growth; damage can take a few days to show, and some plants recover. Follow plant-specific advice.

Avoid unattended heaters, open flames or electrical equipment not designed for outdoor use under covers or in greenhouses, and follow the safety instructions for any heater you do use.

Protecting outdoor pipes, faucets and irrigation

Water expands when it freezes, so outdoor plumbing is at risk once nights fall below freezing. General steps many homeowners take before the first hard freeze include:

• Disconnect and drain garden hoses and store them, so water is not trapped against the faucet.
• Shut off and drain outdoor faucets from the indoor shut-off valve if your home has one, then open the outdoor tap to let water drain.
• Insulate exposed pipes in unheated areas such as crawl spaces, garages and exterior walls, and consider insulated covers for outdoor faucets.
• Drain or winterise irrigation systems and backflow devices according to the manufacturer’s instructions, or have a qualified professional do it.
• Empty water features, rain barrels and containers that could crack.
• Monitor unheated spaces. A Wi‑Fi thermometer with a low-temperature alert in a garage, crawl space or vacation home can warn you that pipes are at risk if the heating fails.

Plumbing set-ups differ, so follow your local building guidance and the instructions for your fixtures, and call a licensed plumber if you are unsure.

First frost, last frost and the growing season

The last frost date is the spring counterpart: the estimated date after which frost becomes unlikely. The period between the average last spring frost and the average first autumn frost is often called the frost-free period or growing season, and seed packets and planting guides use it to say whether a crop has time to mature. The same caveats apply: these are probabilities from long-term records, and your yard may differ. Climate normals data often includes spring and autumn freeze information together, so the same lookup serves both.

Build your own frost record

The best frost date for your garden is the one you measure. Each autumn, note the date of your first frost (what you saw on plants and surfaces) and your first freeze (what your thermometer recorded at sensor height), along with the overnight minimum and the conditions: clear or cloudy, calm or windy. Do the same for the last frost in spring. A station or Wi‑Fi sensor with history can do the recording for you; a notebook and a min/max thermometer work too.

After a few years you will see how your garden compares with the official estimate and how much it varies year to year. That record is more useful than any single published date, and it makes the decision on a borderline night much easier. If you want to start measuring, the outdoor thermometer guide covers placement, and the wireless weather station and Wi‑Fi weather station guides explain systems with remote sensors, history and alerts.