If you garden in Connecticut, the working numbers are simple: expect a last spring frost sometime between April 2 and April 12, and a first fall frost between October 28 and November 10. Those dates come from the Bridgeport coastal weather station, which runs milder than most of the state, so treat them as a starting point rather than a guarantee for your own yard.
The frost dates for Connecticut
These figures come from NOAA’s National Centers for Environmental Information, using the 1991-2020 Climate Normals for station USW00094702 in Bridgeport. The agency doesn’t publish a single “frost day” the way an almanac might. Instead it calculates the probability that the temperature drops to 32°F on any given date, then reports the window where that probability sits between 30% and 70%. That’s why you see a range instead of one tidy date.
In practical terms: on April 2, there’s roughly a 30% chance of a freeze that morning. By April 12, that risk has climbed toward 70%. Flip the logic for fall: by October 28, freeze odds are around 30% and climbing, reaching about 70% by November 10. Neither end of the range is a hard cutoff. A freeze can and does happen outside that window, just less often.
| Event | Date range | Meaning |
|---|---|---|
| Last spring frost | April 2 to April 12 | 32°F freeze probability moves from 30% to 70% |
| First fall frost | October 28 to November 10 | 32°F freeze probability moves from 30% to 70% |
Bridgeport sits on Long Island Sound, and that water moderates temperatures in both directions, it delays the first fall frost and pulls the last spring frost earlier. The USDA Plant Hardiness Zone Map, a separate system built on a single measurement (the average annual extreme minimum winter temperature, using 1991-2020 normals), places Connecticut across zones 6a to 7b. That’s a wide spread for a small state, and it tells you about winter cold, not about your planting calendar. For week-by-week planting decisions, the frost date window matters more than the zone number.
How long the growing season actually is here
Subtract the last spring frost from the first fall frost and you get the frost-free growing season, at least for the Bridgeport station. Run the math on the earliest combination (last frost April 2, first frost November 10) and you get a season stretching to about 222 days. Run it on the more conservative pairing (last frost April 12, first frost October 28) and the season shrinks to roughly 199 days. Most years fall somewhere in that 199 to 222-day band, closer to 210 days on average.
That’s a meaningfully long season by New England standards, and it’s a direct result of coastal warmth. A gardener working from these Bridgeport-based numbers in an inland or hill-town setting is likely overestimating their actual frost-free window, sometimes by several weeks on both ends.
What that season length supports
Around 200 days of frost-free growing is enough to run a full sequence: cool-season crops in early spring, a full summer of heat-loving vegetables like tomatoes and peppers, and often a second round of quick-maturing greens or roots before the fall frost shuts things down. Crops with long maturity windows, think winter squash or certain dry beans, need most of that season and leave little room for a late start.
The gap between the shortest and longest estimated season, about 23 days, is exactly why gardeners hedge their bets. Starting seeds indoors, using row cover, or choosing shorter-maturity varieties are all ways of buying insurance against a season landing on the shorter end of that range.
Turning these dates into a sowing date
Seed packets and extension guides usually frame planting instructions around the last spring frost date, not a calendar day. A packet that says “start indoors 6 to 8 weeks before last frost” is telling you to count backward from your local last-frost estimate. Using the Bridgeport range as an example, that puts indoor seed-starting for tomatoes or peppers sometime between mid-February and late February, if you’re gardening in a similarly mild coastal setting.
Direct-seeding outdoors follows a different logic depending on the crop’s cold tolerance:
- Cold-hardy crops (peas, spinach, lettuce): can go in the ground several weeks before the last frost date, since a light freeze rarely kills them.
- Tender crops (tomatoes, peppers, squash, beans): should wait until after the last frost date has passed, since even a brief freeze will damage or kill them.
- Fall crops (many root vegetables, brassicas): get timed backward from the first fall frost date, counting the days to maturity listed on the seed packet.
For fall plantings, the math runs in reverse. If a crop needs 60 days to mature and your first fall frost estimate is October 28, the seed needs to go in by roughly the start of September, with a little cushion built in since growth slows as daylight shortens through late summer and early fall.
None of this replaces a local check. The University of Connecticut’s Cooperative Extension Service (extension.uconn.edu) is the land-grant resource for county-level planting guidance, soil testing, and crop-specific advice tailored to Connecticut conditions rather than a single coastal station.
Why your own garden differs from this figure
The Bridgeport station sits right on Long Island Sound, and that placement matters more than most gardeners realize. Large bodies of water absorb heat slowly and release it slowly, which softens temperature swings nearby. Move even a few miles inland and that buffering effect fades fast.
Connecticut’s interior and northwest corner, the hill towns around Litchfield County for example, sit at higher elevation and farther from the Sound’s moderating influence. Freezes there tend to arrive earlier in fall and linger later into spring than the Bridgeport figures suggest. A gardener working from coastal data alone in that part of the state risks planting tender crops too early or leaving them exposed to an early fall freeze that never touched Bridgeport at all.
Beyond the broad coastal-versus-inland divide, small features around a specific property shift frost timing further. Low spots and valley bottoms collect cold air on still nights, since cold air is denser and sinks, and those spots often see frost when a slope 50 feet away stays clear. Urban and suburban areas hold heat from pavement and buildings, creating a mild pocket that can push frost dates later, an effect sometimes called an urban heat island. Wind exposure, tree cover, and even the color of nearby surfaces all nudge a garden’s actual frost timing away from the regional average.
The published range is a regional signal, not a site-specific forecast. Gardeners serious about pinning down their own numbers often keep a simple log of First and Last Frost observations at their own property over several years, which ends up being more useful than any station-based estimate.
Common questions
Is the Bridgeport frost date the same for the whole state?
No. Bridgeport is a coastal station and the mildest reference point in Connecticut. Inland and northwest areas typically see later last-spring frosts and earlier first-fall frosts than the Bridgeport range.
What does the 30-70% probability band actually mean for planting?
It means the frost risk is transitioning during that window rather than switching off on a single day. Early in the range, freeze risk is still meaningful; by the end of the range, freeze has usually become unlikely.
Does the USDA hardiness zone tell me when to plant?
No. The hardiness zone (6a-7b across Connecticut) is based on the average annual extreme minimum winter temperature and is meant to guide perennial plant selection, not spring or fall planting timing.
Where can I get frost guidance specific to my county?
The University of Connecticut’s Cooperative Extension Service (extension.uconn.edu) offers county-level resources that account for local conditions the statewide station data can’t capture.