What does this frost date finder show?
This tool looks up two dates for your area: the last freeze of spring and the first freeze of fall. Each one is shown at three probability levels, because freeze dates are not fixed. They shift by a week or more from year to year, and the median date is simply the middle of that spread.
You also get the length of the typical growing season, which is the number of days between the median spring freeze and the median fall freeze. That single number tells you whether long-season crops like watermelon or storage onions have enough time to finish before cold returns.
The three probability levels
Freeze dates come in probabilities because the real date varies every year. The tool shows three levels for each season.
Median (50 percent)
Half of the years on record had the last spring freeze before this date and half after. For fall, half of the years had the first freeze before this date. The median is the standard planning date and the one most planting schedules are built around.
The conservative side
For spring, the "nearly safe" date is the point after which only about 1 in 10 years still has a freeze. Gardeners who do not want to gamble on tender seedlings wait for this date. For fall, the "freeze expected" date is when about 9 in 10 years have already had a freeze, so crops should be harvested or protected well before it.
The risky side
For spring, the "freeze still likely" date is early enough that about 9 in 10 years still get a freeze afterward. Planting tender crops at this date works only in mild years. For fall, the "early freeze possible" date marks when about 1 in 10 years has already frozen, which matters when you are counting backward to set fall sowing dates.
How the dates are found
A ZIP code lookup finds the NOAA weather station nearest your ZIP centroid, then reads that station's freeze date probabilities from the 1991 to 2020 U.S. Climate Normals. The result card names the station and its distance, because a station 40 miles away describes your garden less precisely than one across town.
The freeze threshold is 32 degrees air temperature at standard instrument height. That is stricter than frost. Frost can settle on leaves and rooftops when the official air temperature reads 34 or 35 degrees, so a garden can take frost damage on a night that never registers as a freeze.
Freeze dates are probabilities, not promises
Treat these dates the way a forecaster does. The median is the best single planning date, but in a real garden the useful question is risk tolerance. Hardy crops like peas and spinach can go in while freeze risk is still high because they shrug off light freezes. Tender crops like tomatoes and peppers should wait for the median date at the earliest, and cautious gardeners wait closer to the "nearly safe" date.
Your own garden can also differ from the station. Low spots collect cold air, pavement and walls hold heat, and slopes drain frost downhill. Two gardens in the same ZIP code can be a week apart.
Common mistakes with frost dates
Treating the median as a guarantee
The median means the freeze happens earlier half the time. For tender crops, that is a coin flip. Planting tomatoes on the median date works most years, but the years it fails are expensive.
Confusing frost with freeze
Frost appears when surfaces radiate heat on calm, clear nights, even when the air stays a few degrees above freezing. The dates here track a 32 degree air temperature, so tender plants can still take damage on nights that technically were not a freeze.
Ignoring the fall date
Most gardeners watch only the spring date. The first fall freeze sets the deadline for warm-season harvests and the anchor for counting backward to fall sowings. Crops planted too late in summer run out of growing season before they size up.
Assuming the zone tells the same story
The USDA hardiness zone describes average winter minimums for perennial survival, not when the last spring freeze falls. Two places can share a zone and have very different freeze dates.
Worked examples
A gardener in zone 7b
The lookup returns a median last freeze of April 2 and a median first freeze of November 2. The growing season is about 214 days, long enough for melons, sweet potatoes, and a full fall garden. The "nearly safe" spring date of April 16 is when tender transplants can go out without watching the forecast.
A gardener in zone 4b
The median last freeze is May 12 and the median first freeze lands in late September, leaving roughly 130 frost-free days. That season fits tomatoes and peppers started indoors, but long-season melons are a stretch. The early fall freeze probability matters here: a freeze by September 20 happens about 1 in 10 years, so tender crops need protection plans from mid September on.
Where our data comes from
Freeze dates come from the NOAA NCEI U.S. Climate Normals for 1991 to 2020, specifically the dates at which the probability of a 32 degree minimum temperature falls to 90, 50, and 10 percent. The ZIP code's USDA hardiness zone comes from the 2023 Plant Hardiness Zone data published by the PRISM Climate Group, and place names come from GeoNames postal data. The site picks the nearest station with valid first and last freeze records. These are historical normals, so they describe the climate, not this week's forecast. Check a current forecast before acting on a specific night.
Frequently asked questions
Which probability should I plant by? The median is the 50/50 date: half of years freeze later, half earlier. Tender plants you cannot easily replace go in after the conservative date. Crops you can replant cheaply can go in earlier at the median or the risky side.
Is the fall freeze date the end of the season? Not for hardy crops. Kale, spinach, and carrots shrug off light freezes and keep growing under cover. The fall date matters most for tender crops that die at the first real frost, like tomatoes and basil.
Why do my dates differ from a nearby town's? Each ZIP is matched to the nearest NOAA station, and stations sit at different elevations and exposures. Urban heat islands and cold air drainage can also shift the real date by a week or more between nearby gardens.
