USDA Hardiness Zone 7a
Frost Dates for 63121 — Saint Louis, Missouri
NOAA 1991–2020 normals from St Louis Lambert International Airport, MO (531 ft), 5 miles northwest.
Updated
In Saint Louis, the last spring frost (32°F) is around April 2 in half of years and has passed by April 17 in nine years out of ten. The first fall frost comes around November 4, as early as October 23 one year in ten, leaving a typical freeze-free season of 215 days (NOAA, St Louis Lambert International Airport, MO).
- Last spring frost
- April 2
- First fall frost
- November 4
- Growing season
- 215 days
- Hardiness zone
- 7a
50% probability
50% probability
freeze-free, 50%
0 to 5°F (-17.8 to -15.0°C) coldest night
- First snow
- December 2
- Last snow
- March 17
- Winters with snow
- 100%
- Snow per year
- 16.6"
median, 1991–2020
median, 1991–2020
30 of 30 observed
NOAA normal
Frost risk by date in Saint Louis
Half of springs at St Louis Lambert International Airport, MO see their last 32°F night by April 2; only one in ten is past it by March 17, and one in ten still has one after April 17. Planting tender crops after April 7 leaves a 30% risk of a frost on them, after April 11 20%, and after April 17 10%. The 15 days between the even-odds date and the one-in-ten date is narrower than at 54% of the 158 Missouri stations behind this site's ZIP pages.
In fall the first 32°F night comes by November 4 in half of years, as early as October 23 one year in ten, and holds off past November 18 one year in ten. A hard freeze of 28°F follows 9 days later, around November 13; in spring the one-in-ten date for 28°F is April 7, 10 days before the 32°F one. The freeze-free season lasts 215 days in a typical year, longer than at 93% of the 158 Missouri stations; it reaches 236 days one year in ten and falls short of 196 one year in ten. On average 85 nights a year drop to 32°F or below. Nights of 36°F, when frost can still settle on leaves in low, open spots, continue 11 days longer, to about April 13, and return around October 26. Severe cold of 16°F or below comes every winter, usually between December 16 and February 25.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Mar 31 | Apr 3 | Apr 7 | Apr 9 | Apr 13 | Apr 16 | Apr 19 | Apr 23 | Apr 28 |
| 32°F | Mar 17 | Mar 24 | Mar 28 | Mar 31 | Apr 2 | Apr 5 | Apr 7 | Apr 11 | Apr 17 |
| 28°F | Mar 5 | Mar 12 | Mar 17 | Mar 20 | Mar 23 | Mar 27 | Mar 31 | Apr 3 | Apr 7 |
| 24°F | Feb 24 | Mar 1 | Mar 5 | Mar 9 | Mar 12 | Mar 15 | Mar 18 | Mar 23 | Mar 29 |
| 20°F | Feb 12 | Feb 20 | Feb 26 | Mar 2 | Mar 4 | Mar 7 | Mar 10 | Mar 14 | Mar 18 |
| 16°F | Feb 1 | Feb 9 | Feb 14 | Feb 20 | Feb 25 | Mar 1 | Mar 5 | Mar 9 | Mar 14 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Oct 14 | Oct 18 | Oct 20 | Oct 23 | Oct 26 | Oct 28 | Oct 30 | Nov 2 | Nov 6 |
| 32°F | Oct 23 | Oct 27 | Oct 30 | Nov 1 | Nov 4 | Nov 6 | Nov 9 | Nov 12 | Nov 18 |
| 28°F | Nov 2 | Nov 5 | Nov 8 | Nov 11 | Nov 13 | Nov 16 | Nov 20 | Nov 24 | Nov 30 |
| 24°F | Nov 8 | Nov 13 | Nov 16 | Nov 20 | Nov 24 | Nov 27 | Dec 1 | Dec 5 | Dec 11 |
| 20°F | Nov 17 | Nov 23 | Nov 27 | Dec 1 | Dec 4 | Dec 8 | Dec 12 | Dec 17 | Dec 23 |
| 16°F | Nov 27 | Dec 1 | Dec 7 | Dec 11 | Dec 16 | Dec 21 | Dec 25 | Dec 29 | Jan 6 |
Freeze probabilities 1991–2020 at St Louis Lambert International Airport, MO, from NOAA NCEI U.S. Climate Normals. Where a temperature is reached in fewer than 99.5% of years, the dates describe only the years that reach it. Not a forecast.
Frost risk on any date in 63121 →Compare Saint Louis with another place →
Weather by month in Saint Louis
July is the warmest month at St Louis Lambert International Airport, MO, averaging 90°F by day and 71°F at night; January is the coldest at 40°F and 24°F. A freezing night is all but certain in every month from November to March (a 90% chance or more). From May to September the chance of a 32°F night stays under 10% each month. In spring, April still brings one in 58% of years.
Warmth for growing adds up to 4,590 growing degree days a year (base 50°F), more than at 92% of the 158 Missouri stations. 38% of them (1,724) have built up by the end of June, and July adds the most, 941. Precipitation totals 41.7 inches a year, most in May (4.8") and least in February (2.2"); May to September bring 47% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 40 | 24 | 2.6 | 100% | 24 | 7 |
| Feb | 46 | 28 | 2.2 | 100% | 19 | 20 |
| Mar | 57 | 37 | 3.5 | 99% | 10 | 94 |
| Apr | 68 | 47 | 4.7 | 58% | 1 | 264 |
| May | 77 | 58 | 4.8 | 0% | 0 | 543 |
| Jun | 86 | 67 | 4.5 | 0% | 0 | 796 |
| Jul | 90 | 71 | 3.9 | 0% | 0 | 941 |
| Aug | 88 | 69 | 3.4 | 0% | 0 | 893 |
| Sep | 81 | 61 | 3.0 | 0% | 0 | 630 |
| Oct | 69 | 49 | 3.2 | 35% | 1 | 308 |
| Nov | 56 | 37 | 3.4 | 100% | 9 | 81 |
| Dec | 45 | 29 | 2.5 | 100% | 20 | 14 |
Monthly normals 1991–2020 at St Louis Lambert International Airport, MO (531 ft), NOAA NCEI. "32°F night": chance of at least one in the month. GDD: growing degree days, base 50°F.
Compared with the next station
The nearest other station, St Louis Sci Ctr, MO, 5 miles south of Saint Louis, has a last frost 1 day earlier (April 1), the same first-frost date, a season 3 days longer.
When it snows in Saint Louis, Missouri
The first measurable snow (0.1 inch or more) in Saint Louis usually arrives around December 2, and the last of the season around March 17. Those are the middle dates across the winters of 1991–2020 at St Louis Lambert International Airport, MO, 5.3 miles away: half of years saw snow earlier, half later. Every one of those winters saw snow. The last 32°F night of spring typically comes 16 days after the last snow.
Planting calendar for 63121
| When | What to do |
|---|---|
| January 22 – February 5 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| February 5 – February 19 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| March 5 – March 19 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| April 2 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by August 12 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by October 21 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| November 4 onward | Plant garlic, mulch beds, lift tender bulbsGarlic wants a cold spell; bare soil loses structure over winter. |
The weeks before and after the 50% dates are general rules of thumb, not NOAA figures; a seed packet gives the timing for each variety.
Where these figures come from
ZIP 63121 is 5 miles from St Louis Lambert International Airport, MO, which stands at 531 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 13 other ZIP codes share the station; its figures are presented in full for 63031 (Florissant). The 2023 USDA Plant Hardiness Zone Map lists ZIP 63121 in zone 7a, the band where the coldest night of the year averaged 0 to 5°F (-17.8 to -15.0°C) over 1991–2020; a zone describes winter lows, not frost dates.
Hardiness zone and temperature range: USDA Plant Hardiness Zone Map 2023 (USDA-ARS, Oregon State University), ZIP-code listing, unchanged. °C converted from °F by this site.
Thirty-year averages, not a forecast: check the forecast before planting out. How stations are matched and which pages are offered to search engines: methodology.