USDA Hardiness Zone 5b
Frost Dates for 50228 — Prairie City, Iowa
NOAA 1991–2020 normals from Des Moines 17 E, IA (921 ft), 3 miles southwest.
Updated
In Prairie City, the last spring frost (32°F) is around April 21 in half of years and has passed by May 5 in nine years out of ten. The first fall frost comes around October 15, as early as September 30 one year in ten, leaving a typical freeze-free season of 174 days (NOAA, Des Moines 17 E, IA).
- Last spring frost
- April 21
- First fall frost
- October 15
- Growing season
- 174 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
- November 29
- Last snow
- March 20
- Winters with snow
- 100%
- Snow per year
- 28.7"
median, 1991–2020
median, 1991–2020
26 of 26 observed
NOAA normal
Frost risk by date in Prairie City
Half of springs at Des Moines 17 E, IA see their last 32°F night by April 21; only one in ten is past it by April 7, and one in ten still has one after May 5. Planting tender crops after April 28 leaves a 30% risk of a frost on them, after May 1 20%, and after May 5 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 15 in half of years, as early as September 30 one year in ten, and holds off past October 27 one year in ten. A hard freeze of 28°F follows 10 days later, around October 25; in spring the one-in-ten date for 28°F is April 26, 9 days before the 32°F one. The freeze-free season lasts 174 days in a typical year, longer than at 79% of the 132 Iowa stations; it reaches 193 days one year in ten and falls short of 154 one year in ten. On average 137 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 May 2, and return around October 3. Severe cold of 16°F or below comes every winter, usually between November 20 and March 13.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 18 | Apr 22 | Apr 26 | Apr 30 | May 2 | May 4 | May 7 | May 10 | May 15 |
| 32°F | Apr 7 | Apr 11 | Apr 15 | Apr 18 | Apr 21 | Apr 24 | Apr 28 | May 1 | May 5 |
| 28°F | Mar 29 | Apr 2 | Apr 5 | Apr 8 | Apr 10 | Apr 13 | Apr 16 | Apr 20 | Apr 26 |
| 24°F | Mar 16 | Mar 23 | Mar 28 | Mar 31 | Apr 2 | Apr 4 | Apr 7 | Apr 10 | Apr 17 |
| 20°F | Mar 6 | Mar 11 | Mar 16 | Mar 20 | Mar 23 | Mar 26 | Mar 30 | Apr 2 | Apr 7 |
| 16°F | Feb 27 | Mar 3 | Mar 7 | Mar 10 | Mar 13 | Mar 16 | Mar 19 | Mar 23 | Mar 30 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 19 | Sep 24 | Sep 28 | Oct 1 | Oct 3 | Oct 6 | Oct 9 | Oct 12 | Oct 17 |
| 32°F | Sep 30 | Oct 5 | Oct 10 | Oct 13 | Oct 15 | Oct 18 | Oct 21 | Oct 24 | Oct 27 |
| 28°F | Oct 13 | Oct 17 | Oct 21 | Oct 23 | Oct 25 | Oct 28 | Oct 30 | Nov 1 | Nov 6 |
| 24°F | Oct 23 | Oct 27 | Oct 30 | Nov 1 | Nov 3 | Nov 5 | Nov 8 | Nov 12 | Nov 16 |
| 20°F | Nov 1 | Nov 3 | Nov 6 | Nov 8 | Nov 11 | Nov 15 | Nov 18 | Nov 22 | Nov 29 |
| 16°F | Nov 6 | Nov 10 | Nov 14 | Nov 17 | Nov 20 | Nov 24 | Nov 28 | Dec 2 | Dec 7 |
Freeze probabilities 1991–2020 at Des Moines 17 E, 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 50228 →Compare Prairie City with another place →
Weather by month in Prairie City
July is the warmest month at Des Moines 17 E, IA, averaging 84°F by day and 64°F at night; January is the coldest at 30°F and 13°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 21% of years.
Warmth for growing adds up to 3,131 growing degree days a year (base 50°F), more than at 65% of the 132 Iowa stations. 36% of them (1,117) have built up by the end of June, and July adds the most, 733. Precipitation totals 36.6 inches a year, most in June (5.6") and least in January (1.0"); May to September bring 59% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 30 | 13 | 1.0 | 100% | 30 | 0 |
| Feb | 35 | 17 | 1.4 | 100% | 26 | 3 |
| Mar | 49 | 28 | 2.3 | 100% | 21 | 34 |
| Apr | 62 | 39 | 3.8 | 98% | 7 | 125 |
| May | 71 | 51 | 4.8 | 21% | 1 | 349 |
| Jun | 80 | 61 | 5.6 | 0% | 0 | 606 |
| Jul | 84 | 64 | 3.9 | 0% | 0 | 733 |
| Aug | 82 | 61 | 4.2 | 0% | 0 | 673 |
| Sep | 76 | 53 | 3.2 | 11% | <1 | 434 |
| Oct | 63 | 41 | 2.9 | 96% | 6 | 155 |
| Nov | 48 | 29 | 1.9 | 100% | 18 | 19 |
| Dec | 35 | 19 | 1.6 | 100% | 28 | 1 |
Monthly normals 1991–2020 at Des Moines 17 E, IA (921 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, Newton, IA, 14 miles northeast of Prairie City, has a last frost 1 day later (April 22), a first frost 2 days later (October 17).
When it snows in Prairie City, Iowa
The first measurable snow (0.1 inch or more) in Prairie City usually arrives around November 29, and the last of the season around March 20. Those are the middle dates across the winters of 1991–2020 at Newton, IA, 14 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 50228
| When | What to do |
|---|---|
| February 10 – February 24 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| February 24 – March 10 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| March 24 – April 7 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| April 21 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 23 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by October 1 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 15 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 50228 is 3 miles from Des Moines 17 E, IA, which stands at 921 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 5 other ZIP codes share the station; its figures are presented in full for 50009 (Altoona). The 2023 USDA Plant Hardiness Zone Map lists ZIP 50228 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.