Missouri’s last spring frost falls somewhere between April 6 and April 20, and the first fall frost typically shows up between October 18 and October 29, according to NOAA’s 1991-2020 climate normals for the Kansas City station. That’s roughly six months of frost-free growing, though the real number for your yard depends heavily on where in the state you garden and how your particular patch of ground behaves.
The frost dates for Missouri
The numbers above come from a specific dataset: NOAA NCEI’s 1991-2020 Climate Normals, calculated from 30-year freeze probability records at station USW00003947, which sits at Kansas City International Airport (MCI). The “30-70% band” language matters here. It means there’s still roughly a 30% chance of a 32°F freeze occurring on the early side of that window, and by the late side, the odds have climbed to about 70%. In plain terms, April 6 isn’t a guarantee, it’s the point where frost risk starts dropping fast, and April 20 is where it’s mostly, but not entirely, gone.
USDA’s Plant Hardiness Zone Map, built from the same 1991-2020 normals, places Missouri across a wide 5b to 7b range. That system measures exactly one thing: the average annual extreme minimum temperature at a location. It says nothing about when your last spring frost lands or how long your growing season runs, so treat the zone number as a separate piece of information, not a substitute for the frost dates above.
Why the station location matters
MCI sits well north of downtown Kansas City, in more open terrain that cools faster than the urban core. That geographic quirk shifts the numbers. The downtown station runs about five days earlier in spring than the MCI figures cited above, meaning gardeners closer to the city center typically see their last frost sooner. Head further south in the state and the picture gets milder still, though exact day counts for those areas aren’t part of this dataset.
| Location | Spring pattern | Fall pattern |
|---|---|---|
| MCI (reference station used above) | April 6-20 | October 18-29 |
| Downtown Kansas City | About 5 days earlier | Not published in this dataset |
| Southern Missouri | Milder, earlier still | Milder, later still |
That table isn’t a set of firm dates for the second and third rows. It’s a reminder that a single airport station, however well-documented, describes one point on the map. Missouri stretches roughly 300 miles from its Iowa border to its Arkansas line, and frost doesn’t arrive on the same schedule across that distance.
How long the growing season actually is here
Pairing the two frost windows gives a rough range for the frost-free season. Take the latest possible last frost (April 20) against the earliest possible first fall frost (October 18), and you get a shorter-season scenario of about 181 days. Flip it around, using the earliest spring frost (April 6) and the latest fall frost (October 29), and the season stretches to roughly 206 days. Most years land somewhere between those two figures, which works out to a little under six months on the short end and closer to seven on the long end.
That’s a wide swing for one climate zone, and it explains why two gardeners in the same county can have very different luck with the same crop in the same year. A tomato variety that needs 100 days to mature has plenty of room in either scenario. Something that needs 140 days, a few winter squash varieties or certain dry beans, is cutting it close in the shorter version of the season and comfortable in the longer one.
What this means for crop selection
Seed packets and plant tags list “days to maturity,” and that number should get compared against the shorter end of the local season estimate, not the longer one. Betting on 206 frost-free days when your particular spot tends to run closer to 181 is how a first frost catches a crop still weeks from ready. Gardeners running season extension methods, row covers, cold frames, or simply a south-facing wall that holds heat, can push both edges of that window a little further than the raw numbers suggest, but that’s an adjustment on top of the baseline, not a replacement for knowing what the baseline actually is.
Turning these dates into a sowing date
The frost windows are most useful as anchor points for counting backward and forward. For warm-season crops, tomatoes, peppers, squash, and anything else that can’t tolerate a freeze, treat the later end of the spring window, April 20, as the safer transplant date rather than the earlier one. Setting plants out on April 6 means gambling against that 30% frost probability, and a single cold night can wipe out weeks of indoor growing effort.
Seed packets for those same crops usually recommend starting indoors six to eight weeks before the expected transplant date. Counting back from April 20 lands seed-starting somewhere in late February to early March for most warm-season vegetables, which lines up with how Missouri gardeners typically time their indoor setups.
Cool-season crops flip the calendar. Peas, spinach, lettuce, and other cold-tolerant vegetables can go in the ground several weeks before the last frost date, since a light freeze doesn’t damage them the way it kills tomatoes or peppers. Many gardeners direct-sow these as early as late March in the milder parts of the state, watching soil temperature and workability more than the calendar.
Working backward from the fall frost
Fall plantings need the same math run in reverse. If a crop needs 60 days to mature and the first fall frost is expected around October 18, seeds or transplants need to go in by late August at the latest, and earlier is safer given that a killing frost can arrive before the average date in a cold year. This is also where local knowledge starts to matter more than any published number. The University of Missouri Extension service (extension.missouri.edu) maintains county-level offices that track local planting windows and can speak to conditions in a specific area far than a statewide dataset ever will.
Why your own garden differs from this figure
A backyard is not a weather station. Elevation alone can shift frost timing by days: cold air is denser than warm air, so it flows downhill and pools in low spots, creating what gardeners call frost pockets. A vegetable bed at the bottom of a slope can see frost weeks before a bed thirty feet away on higher ground.
Urban heat plays a role too, and it’s part of why the MCI-versus-downtown gap exists in the first place. Pavement, buildings, and concentrated structures hold daytime heat and release it slowly overnight, which is exactly why the downtown Kansas City station trends about five days earlier in spring than the airport figures. A garden tucked against a south-facing brick wall, or surrounded by pavement rather than open field, behaves more like that warmer downtown reading than like the airport baseline.
Tree canopy, water features, and even fencing that blocks cold wind can nudge the numbers further. None of this means the NOAA figures are wrong, they’re accurate for the specific station they measure. It means treating April 6-20 and October 18-29 as a starting frame rather than a guarantee for a particular yard. Keeping a simple frost log, jotting down the actual date of the first and last freeze each year for a specific garden, builds a far more useful personal dataset over three or four seasons than any regional average can provide on its own.
Common questions
What USDA hardiness zone is Missouri in?
Missouri spans USDA zones 5b through 7b, based on the 2023 Plant Hardiness Zone Map built from 1991-2020 normals. That range reflects average extreme minimum winter temperatures, not frost timing, so a gardener still needs the separate spring and fall frost windows to plan a planting calendar.
When is it safe to plant tomatoes in Missouri?
Based on the Kansas City area data, waiting until the later part of the spring frost window, around April 20, gives a meaningfully lower risk than planting at the earlier edge on April 6. Gardeners in milder southern parts of the state, or in warmer urban microclimates, sometimes have room to move earlier, but that specific date isn’t published in this dataset.
How many frost-free days does Missouri typically get?
Combining the two published windows puts the frost-free season somewhere between about 181 and 206 days, depending on where the actual last spring frost and first fall frost fall in a given year. That’s a derived range built from the NOAA station data, not a separately published figure.
Are frost dates the same across Kansas City, St. Louis, and southern Missouri?
No. The dates cited here come from the MCI station near Kansas City. Downtown Kansas City runs about five days earlier in spring, and southern Missouri tends to be milder in both directions, though exact figures for St. Louis or the southern part of the state aren’t included in this dataset. Local extension offices are the best resource for site-specific numbers.