USDA Hardiness Zone 5b
Frost Dates for 50854 — Mount Ayr, Iowa
NOAA 1991–2020 normals from Mt Ayr, IA (1,140 ft), under a mile west.
Updated
In Mount Ayr, the last spring frost (32°F) is around April 25 in half of years and has passed by May 9 in nine years out of ten. The first fall frost comes around October 12, as early as September 27 one year in ten, leaving a typical freeze-free season of 169 days (NOAA, Mt Ayr, IA).
- Last spring frost
- April 25
- First fall frost
- October 12
- Growing season
- 169 days
- Hardiness zone
- 5b
50% probability
50% probability
freeze-free, 50%
-15 to -10°F (-26.1 to -23.3°C) coldest night
- First snow
- December 5
- Last snow
- March 10
- Winters with snow
- 100%
- Snow per year
- 20.5"
median, 1991–2020
median, 1991–2020
30 of 30 observed
NOAA normal
Frost risk by date in Mount Ayr
Half of springs at Mt Ayr, IA see their last 32°F night by April 25; only one in ten is past it by April 10, and one in ten still has one after May 9. Planting tender crops after May 1 leaves a 30% risk of a frost on them, after May 4 20%, and after May 9 10%. The 14 days between the even-odds date and the one-in-ten date is wider than at 58% of the 132 Iowa stations behind this site's ZIP pages.
In fall the first 32°F night comes by October 12 in half of years, as early as September 27 one year in ten, and holds off past October 25 one year in ten. A hard freeze of 28°F follows 11 days later, around October 23; in spring the one-in-ten date for 28°F is April 29, 10 days before the 32°F one. The freeze-free season lasts 169 days in a typical year, longer than at 67% of the 132 Iowa stations; it reaches 188 days one year in ten and falls short of 149 one year in ten. On average 143 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 4, and return around October 1. Severe cold of 16°F or below comes every winter, usually between November 18 and March 16.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 21 | Apr 26 | Apr 29 | May 2 | May 4 | May 8 | May 10 | May 14 | May 20 |
| 32°F | Apr 10 | Apr 15 | Apr 18 | Apr 21 | Apr 25 | Apr 27 | May 1 | May 4 | May 9 |
| 28°F | Apr 1 | Apr 5 | Apr 8 | Apr 12 | Apr 14 | Apr 17 | Apr 21 | Apr 24 | Apr 29 |
| 24°F | Mar 20 | Mar 27 | Mar 31 | Apr 3 | Apr 6 | Apr 8 | Apr 11 | Apr 15 | Apr 20 |
| 20°F | Mar 8 | Mar 14 | Mar 19 | Mar 23 | Mar 28 | Mar 31 | Apr 3 | Apr 7 | Apr 12 |
| 16°F | Feb 28 | Mar 5 | Mar 9 | Mar 13 | Mar 16 | Mar 19 | Mar 24 | Mar 29 | Apr 3 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 18 | Sep 22 | Sep 26 | Sep 29 | Oct 1 | Oct 4 | Oct 7 | Oct 10 | Oct 14 |
| 32°F | Sep 27 | Oct 1 | Oct 6 | Oct 9 | Oct 12 | Oct 15 | Oct 18 | Oct 21 | Oct 25 |
| 28°F | Oct 9 | Oct 14 | Oct 18 | Oct 21 | Oct 23 | Oct 25 | Oct 28 | Oct 31 | Nov 3 |
| 24°F | Oct 18 | Oct 23 | Oct 26 | Oct 29 | Nov 1 | Nov 2 | Nov 5 | Nov 9 | Nov 14 |
| 20°F | Oct 27 | Nov 1 | Nov 3 | Nov 5 | Nov 8 | Nov 11 | Nov 14 | Nov 19 | Nov 26 |
| 16°F | Nov 3 | Nov 7 | Nov 11 | Nov 14 | Nov 18 | Nov 21 | Nov 26 | Dec 1 | Dec 6 |
Freeze probabilities 1991–2020 at Mt Ayr, 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 50854 →Compare Mount Ayr with another place →
Weather by month in Mount Ayr
July is the warmest month at Mt Ayr, IA, averaging 85°F by day and 64°F at night; January is the coldest at 32°F and 12°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 30% of years.
Warmth for growing adds up to 3,158 growing degree days a year (base 50°F), more than at 68% of the 132 Iowa stations. 34% of them (1,080) have built up by the end of June, and July adds the most, 752. Precipitation totals 37.1 inches a year, most in May (5.4") and least in January (0.7"); May to September bring 62% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 32 | 12 | 0.7 | 100% | 30 | 0 |
| Feb | 37 | 16 | 1.3 | 100% | 26 | 2 |
| Mar | 49 | 28 | 2.2 | 100% | 22 | 32 |
| Apr | 61 | 38 | 3.4 | 99% | 9 | 115 |
| May | 71 | 50 | 5.4 | 30% | 1 | 332 |
| Jun | 80 | 60 | 5.4 | 0% | 0 | 599 |
| Jul | 85 | 64 | 4.4 | 0% | 0 | 752 |
| Aug | 83 | 62 | 4.0 | 0% | 0 | 699 |
| Sep | 76 | 53 | 3.7 | 18% | <1 | 441 |
| Oct | 64 | 40 | 2.9 | 97% | 7 | 161 |
| Nov | 49 | 28 | 2.1 | 100% | 20 | 24 |
| Dec | 37 | 18 | 1.6 | 100% | 29 | 1 |
Monthly normals 1991–2020 at Mt Ayr, IA (1,140 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, Lamoni, IA, 16 miles east of Mount Ayr, has a last frost 8 days earlier (April 17), a first frost 9 days later (October 21), a season 15 days longer.
When it snows in Mount Ayr, Iowa
The first measurable snow (0.1 inch or more) in Mount Ayr usually arrives around December 5, and the last of the season around March 10. Those are the middle dates across the winters of 1991–2020 at Mt Ayr, IA, 0.9 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 46 days after the last snow.
Planting calendar for 50854
| When | What to do |
|---|---|
| February 14 – February 28 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| February 28 – March 14 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| March 28 – April 11 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| April 25 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 20 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 28 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 12 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 50854 is under a mile from Mt Ayr, IA, which stands at 1,140 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 50854 in zone 5b, the band where the coldest night of the year averaged -15 to -10°F (-26.1 to -23.3°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.