USDA Hardiness Zone 5a
Frost Dates for 51360 — Spirit Lake, Iowa
NOAA 1991–2020 normals from Spirit Lake, IA (1,420 ft), 2 miles west.
Updated
In Spirit Lake, the last spring frost (32°F) is around April 28 in half of years and has passed by May 9 in nine years out of ten. The first fall frost comes around October 11, as early as September 27 one year in ten, leaving a typical freeze-free season of 164 days (NOAA, Spirit Lake, IA).
- Last spring frost
- April 28
- First fall frost
- October 11
- Growing season
- 164 days
- Hardiness zone
- 5a
50% probability
50% probability
freeze-free, 50%
-20 to -15°F (-28.9 to -26.1°C) coldest night
- First snow
- November 15
- Last snow
- April 4
- Winters with snow
- 100%
- Snow per year
- 41.5"
median, 1991–2020
median, 1991–2020
22 of 22 observed
NOAA normal
Frost risk by date in Spirit Lake
Half of springs at Spirit Lake, IA see their last 32°F night by April 28; only one in ten is past it by April 14, and one in ten still has one after May 9. Planting tender crops after May 3 leaves a 30% risk of a frost on them, after May 5 20%, and after May 9 10%. The 11 days between the even-odds date and the one-in-ten date is narrower than at 88% of the 132 Iowa stations behind this site's ZIP pages.
In fall the first 32°F night comes by October 11 in half of years, as early as September 27 one year in ten, and holds off past October 24 one year in ten. A hard freeze of 28°F follows 10 days later, around October 21; in spring the one-in-ten date for 28°F is May 2, 7 days before the 32°F one. The freeze-free season lasts 164 days in a typical year, shorter than at 52% of the 132 Iowa stations; it reaches 183 days one year in ten and falls short of 145 one year in ten. On average 149 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 8 days longer, to about May 6, and return around October 1. Severe cold of 16°F or below comes every winter, usually between November 15 and March 24.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 25 | Apr 30 | May 2 | May 4 | May 6 | May 9 | May 11 | May 15 | May 20 |
| 32°F | Apr 14 | Apr 18 | Apr 23 | Apr 26 | Apr 28 | May 1 | May 3 | May 5 | May 9 |
| 28°F | Apr 4 | Apr 9 | Apr 13 | Apr 16 | Apr 19 | Apr 22 | Apr 25 | Apr 29 | May 2 |
| 24°F | Mar 27 | Apr 2 | Apr 4 | Apr 7 | Apr 10 | Apr 12 | Apr 16 | Apr 20 | Apr 25 |
| 20°F | Mar 15 | Mar 22 | Mar 28 | Mar 31 | Apr 3 | Apr 5 | Apr 8 | Apr 12 | Apr 18 |
| 16°F | Mar 8 | Mar 13 | Mar 16 | Mar 19 | Mar 24 | Mar 28 | Apr 1 | Apr 4 | Apr 9 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 18 | Sep 22 | Sep 26 | Sep 28 | Oct 1 | Oct 3 | Oct 6 | Oct 10 | Oct 15 |
| 32°F | Sep 27 | Oct 1 | Oct 4 | Oct 7 | Oct 11 | Oct 14 | Oct 17 | Oct 20 | Oct 24 |
| 28°F | Oct 6 | Oct 13 | Oct 16 | Oct 19 | Oct 21 | Oct 24 | Oct 27 | Oct 30 | Nov 4 |
| 24°F | Oct 17 | Oct 22 | Oct 25 | Oct 28 | Oct 31 | Nov 2 | Nov 5 | Nov 9 | Nov 13 |
| 20°F | Oct 25 | Oct 31 | Nov 2 | Nov 5 | Nov 7 | Nov 10 | Nov 13 | Nov 17 | Nov 22 |
| 16°F | Nov 1 | Nov 5 | Nov 8 | Nov 11 | Nov 15 | Nov 18 | Nov 21 | Nov 24 | Dec 1 |
Freeze probabilities 1991–2020 at Spirit Lake, IA, 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 51360 →Compare Spirit Lake with another place →
Weather by month in Spirit Lake
July is the warmest month at Spirit Lake, IA, averaging 83°F by day and 63°F at night; January is the coldest at 24°F and 7°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 40% of years.
Warmth for growing adds up to 2,751 growing degree days a year (base 50°F), fewer than at 82% of the 132 Iowa stations. 33% of them (918) have built up by the end of June, and July adds the most, 704. Precipitation totals 29.0 inches a year, most in June (4.8") and least in January (0.6"); May to September bring 66% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 24 | 7 | 0.6 | 100% | 31 | 0 |
| Feb | 28 | 11 | 0.6 | 100% | 27 | 0 |
| Mar | 42 | 23 | 1.4 | 100% | 24 | 11 |
| Apr | 56 | 35 | 3.0 | 99% | 10 | 70 |
| May | 68 | 48 | 4.1 | 40% | 1 | 274 |
| Jun | 79 | 59 | 4.8 | 0% | 0 | 563 |
| Jul | 83 | 63 | 3.5 | 0% | 0 | 704 |
| Aug | 80 | 60 | 3.7 | 0% | 0 | 625 |
| Sep | 73 | 52 | 3.0 | 19% | 0 | 387 |
| Oct | 59 | 39 | 2.1 | 97% | 7 | 110 |
| Nov | 42 | 25 | 1.4 | 100% | 20 | 8 |
| Dec | 29 | 13 | 0.8 | 100% | 30 | 0 |
Monthly normals 1991–2020 at Spirit Lake, IA (1,420 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, Milford 4 NW, IA, 5 miles southwest of Spirit Lake, has a last frost 3 days later (May 1), a first frost 5 days earlier (October 6), a season 6 days shorter.
When it snows in Spirit Lake, Iowa
The first measurable snow (0.1 inch or more) in Spirit Lake usually arrives around November 15, and the last of the season around April 4. Those are the middle dates across the winters of 1991–2020 at Spirit Lake, IA, 1.6 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 24 days after the last snow.
Planting calendar for 51360
| When | What to do |
|---|---|
| February 17 – March 3 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 3 – March 17 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| March 31 – April 14 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| April 28 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 19 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 27 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 11 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 51360 is 2 miles from Spirit Lake, IA, which stands at 1,420 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 51360 in zone 5a, the band where the coldest night of the year averaged -20 to -15°F (-28.9 to -26.1°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.