USDA Hardiness Zone 6a
Frost Dates for 48473 — Swartz Creek, Michigan
NOAA 1991–2020 normals from Flint Bishop International Airport, MI (770 ft), 4 miles east.
Updated
In Swartz Creek, the last spring frost (32°F) is around May 6 in half of years and has passed by May 23 in nine years out of ten. The first fall frost comes around October 10, as early as September 26 one year in ten, leaving a typical freeze-free season of 155 days (NOAA, Flint Bishop International Airport, MI).
- Last spring frost
- May 6
- First fall frost
- October 10
- Growing season
- 155 days
- Hardiness zone
- 6a
50% probability
50% probability
freeze-free, 50%
-10 to -5°F (-23.3 to -20.6°C) coldest night
- First snow
- November 15
- Last snow
- April 13
- Winters with snow
- 100%
- Snow per year
- 52.1"
median, 1991–2020
median, 1991–2020
30 of 30 observed
NOAA normal
Frost risk by date in Swartz Creek
Half of springs at Flint Bishop International Airport, MI see their last 32°F night by May 6; only one in ten is past it by April 21, and one in ten still has one after May 23. Planting tender crops after May 13 leaves a 30% risk of a frost on them, after May 18 20%, and after May 23 10%. The 17 days between the even-odds date and the one-in-ten date is wider than at 62% of the 172 Michigan stations behind this site's ZIP pages.
In fall the first 32°F night comes by October 10 in half of years, as early as September 26 one year in ten, and holds off past October 25 one year in ten. A hard freeze of 28°F follows 13 days later, around October 23; in spring the one-in-ten date for 28°F is May 13, 10 days before the 32°F one. The freeze-free season lasts 155 days in a typical year, shorter than at 58% of the 172 Michigan stations; it reaches 177 days one year in ten and falls short of 133 one year in ten. On average 141 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 12 days longer, to about May 18, and return around September 28. Severe cold of 16°F or below comes every winter, usually between November 28 and March 20.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 2 | May 7 | May 11 | May 15 | May 18 | May 22 | May 25 | May 29 | Jun 2 |
| 32°F | Apr 21 | Apr 26 | Apr 30 | May 3 | May 6 | May 9 | May 13 | May 18 | May 23 |
| 28°F | Apr 11 | Apr 16 | Apr 19 | Apr 23 | Apr 26 | Apr 29 | May 2 | May 6 | May 13 |
| 24°F | Mar 30 | Apr 3 | Apr 7 | Apr 10 | Apr 14 | Apr 17 | Apr 20 | Apr 24 | May 1 |
| 20°F | Mar 15 | Mar 21 | Mar 26 | Mar 29 | Apr 1 | Apr 3 | Apr 5 | Apr 10 | Apr 16 |
| 16°F | Mar 6 | Mar 10 | Mar 14 | Mar 17 | Mar 20 | Mar 23 | Mar 27 | Mar 30 | Apr 3 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 15 | Sep 20 | Sep 23 | Sep 26 | Sep 28 | Oct 1 | Oct 3 | Oct 5 | Oct 10 |
| 32°F | Sep 26 | Oct 1 | Oct 4 | Oct 6 | Oct 10 | Oct 12 | Oct 15 | Oct 20 | Oct 25 |
| 28°F | Oct 6 | Oct 12 | Oct 17 | Oct 20 | Oct 23 | Oct 28 | Oct 30 | Nov 2 | Nov 6 |
| 24°F | Oct 20 | Oct 27 | Oct 31 | Nov 2 | Nov 4 | Nov 6 | Nov 9 | Nov 14 | Nov 20 |
| 20°F | Nov 2 | Nov 5 | Nov 9 | Nov 12 | Nov 15 | Nov 19 | Nov 22 | Nov 27 | Dec 2 |
| 16°F | Nov 9 | Nov 15 | Nov 20 | Nov 24 | Nov 28 | Dec 1 | Dec 4 | Dec 9 | Dec 17 |
Freeze probabilities 1991–2020 at Flint Bishop International Airport, MI, 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 48473 →Compare Swartz Creek with another place →
Weather by month in Swartz Creek
July is the warmest month at Flint Bishop International Airport, MI, averaging 82°F by day and 60°F at night; January is the coldest at 30°F and 16°F. A freezing night is all but certain in every month from October to April (a 90% chance or more). From June to August the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 65% of years.
Warmth for growing adds up to 2,586 growing degree days a year (base 50°F), more than at 62% of the 172 Michigan stations. 33% of them (850) have built up by the end of June, and July adds the most, 648. Precipitation totals 32.1 inches a year, most in May (3.7") and least in February (1.7"); May to September bring 51% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 30 | 16 | 2.0 | 100% | 28 | 0 |
| Feb | 33 | 17 | 1.7 | 100% | 26 | 1 |
| Mar | 43 | 25 | 2.0 | 100% | 24 | 16 |
| Apr | 57 | 35 | 3.1 | 100% | 12 | 64 |
| May | 69 | 46 | 3.7 | 65% | 1 | 258 |
| Jun | 78 | 56 | 3.1 | 1% | 0 | 512 |
| Jul | 82 | 60 | 3.4 | 0% | 0 | 648 |
| Aug | 80 | 58 | 3.2 | 0% | 0 | 592 |
| Sep | 73 | 50 | 2.9 | 18% | <1 | 360 |
| Oct | 60 | 40 | 2.8 | 96% | 6 | 115 |
| Nov | 47 | 31 | 2.3 | 100% | 18 | 20 |
| Dec | 35 | 23 | 1.9 | 100% | 26 | 2 |
Monthly normals 1991–2020 at Flint Bishop International Airport, MI (770 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, Flint 7W, MI, 7 miles northeast of Swartz Creek, has a last frost 3 days earlier (May 3), a first frost 3 days later (October 13), a season 7 days longer.
When it snows in Swartz Creek, Michigan
The first measurable snow (0.1 inch or more) in Swartz Creek usually arrives around November 15, and the last of the season around April 13. Those are the middle dates across the winters of 1991–2020 at Flint Bishop International Airport, MI, 4 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 23 days after the last snow.
Planting calendar for 48473
| When | What to do |
|---|---|
| February 25 – March 11 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 11 – March 25 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| April 8 – April 22 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| May 6 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 18 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 26 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 10 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 48473 is 4 miles from Flint Bishop International Airport, MI, which stands at 770 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 4 other ZIP codes share the station; its figures are presented in full for 48439 (Grand Blanc). The 2023 USDA Plant Hardiness Zone Map lists ZIP 48473 in zone 6a, the band where the coldest night of the year averaged -10 to -5°F (-23.3 to -20.6°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.