USDA Hardiness Zone 5a
Frost Dates for 50651 — La Porte City, Iowa
NOAA 1991–2020 normals from Vinton, IA (850 ft), 14 miles southeast.
Updated
In La Porte City, the last spring frost (32°F) is around May 3 in half of years and has passed by May 17 in nine years out of ten. The first fall frost comes around October 3, as early as September 20 one year in ten, leaving a typical freeze-free season of 151 days (NOAA, Vinton, IA).
- Last spring frost
- May 3
- First fall frost
- October 3
- Growing season
- 151 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 24
- Last snow
- March 25
- Winters with snow
- 100%
- Snow per year
- 33.6"
median, 1991–2020
median, 1991–2020
30 of 30 observed
NOAA normal
Frost risk by date in La Porte City
Half of springs at Vinton, IA see their last 32°F night by May 3; only one in ten is past it by April 21, and one in ten still has one after May 17. Planting tender crops after May 9 leaves a 30% risk of a frost on them, after May 12 20%, and after May 17 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 3 in half of years, as early as September 20 one year in ten, and holds off past October 15 one year in ten. A hard freeze of 28°F follows 9 days later, around October 12; in spring the one-in-ten date for 28°F is May 8, 9 days before the 32°F one. The freeze-free season lasts 151 days in a typical year, shorter than at 94% of the 132 Iowa stations; it reaches 169 days one year in ten and falls short of 132 one year in ten. On average 145 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 14, and return around September 26. Severe cold of 16°F or below comes every winter, usually between November 9 and March 25.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 30 | May 5 | May 8 | May 11 | May 14 | May 16 | May 20 | May 23 | May 28 |
| 32°F | Apr 21 | Apr 26 | Apr 29 | May 1 | May 3 | May 6 | May 9 | May 12 | May 17 |
| 28°F | Apr 10 | Apr 15 | Apr 18 | Apr 21 | Apr 25 | Apr 27 | Apr 30 | May 4 | May 8 |
| 24°F | Mar 31 | Apr 4 | Apr 7 | Apr 10 | Apr 13 | Apr 17 | Apr 20 | Apr 25 | Apr 29 |
| 20°F | Mar 17 | Mar 25 | Mar 29 | Apr 1 | Apr 4 | Apr 6 | Apr 9 | Apr 14 | Apr 21 |
| 16°F | Mar 7 | Mar 13 | Mar 17 | Mar 21 | Mar 25 | Mar 28 | Mar 31 | Apr 3 | Apr 9 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 13 | Sep 17 | Sep 20 | Sep 23 | Sep 26 | Sep 28 | Oct 1 | Oct 3 | Oct 6 |
| 32°F | Sep 20 | Sep 25 | Sep 28 | Oct 1 | Oct 3 | Oct 6 | Oct 8 | Oct 11 | Oct 15 |
| 28°F | Sep 29 | Oct 3 | Oct 7 | Oct 10 | Oct 12 | Oct 15 | Oct 18 | Oct 21 | Oct 24 |
| 24°F | Oct 8 | Oct 13 | Oct 17 | Oct 20 | Oct 22 | Oct 25 | Oct 27 | Oct 30 | Nov 3 |
| 20°F | Oct 17 | Oct 23 | Oct 26 | Oct 29 | Oct 31 | Nov 2 | Nov 5 | Nov 8 | Nov 14 |
| 16°F | Oct 29 | Nov 1 | Nov 4 | Nov 7 | Nov 9 | Nov 12 | Nov 16 | Nov 20 | Nov 25 |
Freeze probabilities 1991–2020 at Vinton, 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 50651 →Compare La Porte City with another place →
Weather by month in La Porte City
July is the warmest month at Vinton, IA, averaging 81°F by day and 60°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 63% of years.
Warmth for growing adds up to 2,581 growing degree days a year (base 50°F), fewer than at 94% of the 132 Iowa stations. 35% of them (892) have built up by the end of June, and July adds the most, 645. Precipitation totals 38.1 inches a year, most in June (5.6") and least in January (1.2"); May to September bring 60% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 26 | 8 | 1.2 | 100% | 30 | 0 |
| Feb | 30 | 12 | 1.3 | 100% | 26 | 0 |
| Mar | 44 | 24 | 2.1 | 100% | 22 | 17 |
| Apr | 59 | 35 | 3.9 | 100% | 9 | 78 |
| May | 69 | 47 | 5.0 | 63% | 1 | 273 |
| Jun | 78 | 57 | 5.6 | 0% | 0 | 524 |
| Jul | 81 | 60 | 4.2 | 0% | 0 | 645 |
| Aug | 79 | 58 | 4.2 | 0% | 0 | 573 |
| Sep | 74 | 50 | 3.7 | 38% | <1 | 355 |
| Oct | 60 | 37 | 3.2 | 100% | 7 | 105 |
| Nov | 44 | 25 | 2.1 | 100% | 21 | 11 |
| Dec | 31 | 15 | 1.6 | 100% | 29 | 1 |
Monthly normals 1991–2020 at Vinton, IA (850 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, Waterloo Municipal Airport, IA, 19 miles northwest of La Porte City, has a last frost 6 days earlier (April 27), a first frost 7 days later (October 10), a season 14 days longer.
When it snows in La Porte City, Iowa
The first measurable snow (0.1 inch or more) in La Porte City usually arrives around November 24, and the last of the season around March 25. Those are the middle dates across the winters of 1991–2020 at Vinton, IA, 14.3 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 39 days after the last snow.
Planting calendar for 50651
| When | What to do |
|---|---|
| February 22 – March 8 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 8 – March 22 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| April 5 – April 19 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| May 3 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 11 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 19 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 3 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 50651 is 14 miles from Vinton, IA, which stands at 850 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 2 other ZIP codes share the station; its figures are presented in full for 52349 (Vinton). The 2023 USDA Plant Hardiness Zone Map lists ZIP 50651 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.