USDA Hardiness Zone 5a
Frost Dates for 50601 — Ackley, Iowa
NOAA 1991–2020 normals from Iowa Falls, IA (1,055 ft), 11 miles west.
Updated
In Ackley, the last spring frost (32°F) is around April 28 in half of years and has passed by May 11 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 164 days (NOAA, Iowa Falls, IA).
- Last spring frost
- April 28
- First fall frost
- October 10
- 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 25
- Last snow
- March 27
- Winters with snow
- 100%
- Snow per year
- 27.7"
median, 1991–2020
median, 1991–2020
28 of 28 observed
NOAA normal
Frost risk by date in Ackley
Half of springs at Iowa Falls, IA see their last 32°F night by April 28; only one in ten is past it by April 13, and one in ten still has one after May 11. Planting tender crops after May 3 leaves a 30% risk of a frost on them, after May 7 20%, and after May 11 10%. The 13 days between the even-odds date and the one-in-ten date is narrower than at 42% of the 132 Iowa 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 22 one year in ten. A hard freeze of 28°F follows 10 days later, around October 20; in spring the one-in-ten date for 28°F is May 1, 10 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 147 one year in ten. On average 157 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 9 days longer, to about May 7, and return around September 30. Severe cold of 16°F or below comes every winter, usually between November 17 and March 19.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 25 | Apr 30 | May 3 | May 5 | May 7 | May 9 | May 12 | May 15 | May 20 |
| 32°F | Apr 13 | Apr 17 | Apr 22 | Apr 25 | Apr 28 | May 1 | May 3 | May 7 | May 11 |
| 28°F | Apr 3 | Apr 8 | Apr 11 | Apr 14 | Apr 17 | Apr 20 | Apr 24 | Apr 27 | May 1 |
| 24°F | Mar 22 | Mar 29 | Apr 1 | Apr 4 | Apr 7 | Apr 10 | Apr 13 | Apr 17 | Apr 22 |
| 20°F | Mar 11 | Mar 16 | Mar 20 | Mar 24 | Mar 29 | Apr 1 | Apr 4 | Apr 8 | Apr 14 |
| 16°F | Mar 4 | Mar 8 | Mar 12 | Mar 15 | Mar 19 | Mar 22 | Mar 25 | Mar 30 | Apr 5 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 17 | Sep 22 | Sep 25 | Sep 28 | Sep 30 | Oct 3 | Oct 6 | Oct 9 | Oct 13 |
| 32°F | Sep 26 | Oct 1 | Oct 4 | Oct 7 | Oct 10 | Oct 13 | Oct 15 | Oct 18 | Oct 22 |
| 28°F | Oct 5 | Oct 12 | Oct 15 | Oct 18 | Oct 20 | Oct 23 | Oct 25 | Oct 29 | Nov 2 |
| 24°F | Oct 17 | Oct 22 | Oct 25 | Oct 28 | Oct 30 | Nov 1 | Nov 4 | Nov 7 | Nov 11 |
| 20°F | Oct 28 | Nov 1 | Nov 3 | Nov 5 | Nov 8 | Nov 10 | Nov 14 | Nov 17 | Nov 23 |
| 16°F | Nov 4 | Nov 7 | Nov 11 | Nov 14 | Nov 17 | Nov 20 | Nov 24 | Nov 28 | Dec 2 |
Freeze probabilities 1991–2020 at Iowa Falls, 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 50601 →Compare Ackley with another place →
Weather by month in Ackley
July is the warmest month at Iowa Falls, IA, averaging 83°F by day and 62°F at night; January is the coldest at 26°F and 8°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 41% of years.
Warmth for growing adds up to 2,807 growing degree days a year (base 50°F), fewer than at 73% of the 132 Iowa stations. 34% of them (957) have built up by the end of June, and July adds the most, 699. Precipitation totals 38.2 inches a year, most in June (6.1") and least in January (0.9"); May to September bring 63% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 26 | 8 | 0.9 | 100% | 31 | 0 |
| Feb | 31 | 12 | 1.2 | 100% | 27 | 0 |
| Mar | 44 | 24 | 2.1 | 100% | 25 | 13 |
| Apr | 58 | 35 | 3.8 | 100% | 11 | 75 |
| May | 70 | 48 | 5.6 | 41% | 1 | 295 |
| Jun | 80 | 58 | 6.1 | 0% | 0 | 575 |
| Jul | 83 | 62 | 4.5 | 0% | 0 | 699 |
| Aug | 81 | 60 | 4.4 | 0% | 0 | 628 |
| Sep | 75 | 51 | 3.5 | 19% | <1 | 388 |
| Oct | 62 | 38 | 2.6 | 98% | 9 | 122 |
| Nov | 45 | 26 | 2.0 | 100% | 23 | 13 |
| Dec | 32 | 15 | 1.5 | 100% | 30 | 0 |
Monthly normals 1991–2020 at Iowa Falls, IA (1,055 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, Eldora, IA, 14 miles south of Ackley, has a last frost 1 day earlier (April 27), the same first-frost date, a season 1 day longer.
When it snows in Ackley, Iowa
The first measurable snow (0.1 inch or more) in Ackley usually arrives around November 25, and the last of the season around March 27. Those are the middle dates across the winters of 1991–2020 at Iowa Falls, IA, 10.8 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 32 days after the last snow.
Planting calendar for 50601
| 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 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 50601 is 11 miles from Iowa Falls, IA, which stands at 1,055 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station; its figures are presented in full for 50126 (Iowa Falls). The 2023 USDA Plant Hardiness Zone Map lists ZIP 50601 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.