USDA Hardiness Zone 5a
Frost Dates for 50548 — Humboldt, Iowa
NOAA 1991–2020 normals from Humboldt Wtp, IA (1,100 ft), under a mile east.
Updated
In Humboldt, the last spring frost (32°F) is around April 27 in half of years and has passed by May 7 in nine years out of ten. The first fall frost comes around October 9, as early as September 24 one year in ten, leaving a typical freeze-free season of 166 days (NOAA, Humboldt Wtp, IA).
- Last spring frost
- April 27
- First fall frost
- October 9
- Growing season
- 166 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 14
- Last snow
- April 8
- Winters with snow
- 100%
- Snow per year
- 39"
median, 1991–2020
median, 1991–2020
27 of 27 observed
NOAA normal
Frost risk by date in Humboldt
Half of springs at Humboldt Wtp, IA see their last 32°F night by April 27; only one in ten is past it by April 15, and one in ten still has one after May 7. Planting tender crops after May 1 leaves a 30% risk of a frost on them, after May 4 20%, and after May 7 10%. The 10 days between the even-odds date and the one-in-ten date is the narrowest of the 132 Iowa stations behind this site's ZIP pages, so the end of frost is fairly predictable.
In fall the first 32°F night comes by October 9 in half of years, as early as September 24 one year in ten, and holds off past October 24 one year in ten. A hard freeze of 28°F follows 13 days later, around October 22; in spring the one-in-ten date for 28°F is April 30, 7 days before the 32°F one. The freeze-free season lasts 166 days in a typical year, longer than at 56% of the 132 Iowa stations; it reaches 183 days one year in ten and falls short of 147 one year in ten. On average 152 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 5, and return around September 29. Severe cold of 16°F or below comes every winter, usually between November 14 and March 22.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 23 | Apr 28 | May 1 | May 3 | May 5 | May 7 | May 9 | May 11 | May 15 |
| 32°F | Apr 15 | Apr 18 | Apr 21 | Apr 24 | Apr 27 | Apr 30 | May 1 | May 4 | May 7 |
| 28°F | Apr 6 | Apr 9 | Apr 13 | Apr 15 | Apr 17 | Apr 20 | Apr 22 | Apr 25 | Apr 30 |
| 24°F | Mar 26 | Apr 1 | Apr 4 | Apr 6 | Apr 9 | Apr 11 | Apr 14 | Apr 17 | Apr 21 |
| 20°F | Mar 13 | Mar 20 | Mar 24 | Mar 30 | Apr 1 | Apr 3 | Apr 6 | Apr 9 | Apr 15 |
| 16°F | Mar 6 | Mar 11 | Mar 15 | Mar 18 | Mar 22 | Mar 26 | Mar 30 | Apr 2 | Apr 7 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 17 | Sep 21 | Sep 24 | Sep 27 | Sep 29 | Oct 1 | Oct 4 | Oct 8 | Oct 13 |
| 32°F | Sep 24 | Sep 29 | Oct 2 | Oct 5 | Oct 9 | Oct 13 | Oct 17 | Oct 20 | Oct 24 |
| 28°F | Oct 5 | Oct 12 | Oct 16 | Oct 19 | Oct 22 | Oct 24 | Oct 26 | Oct 30 | Nov 3 |
| 24°F | Oct 18 | Oct 23 | Oct 26 | Oct 29 | Oct 31 | Nov 2 | Nov 4 | Nov 8 | Nov 12 |
| 20°F | Oct 27 | Nov 1 | Nov 3 | Nov 5 | Nov 8 | Nov 10 | Nov 13 | Nov 16 | Nov 21 |
| 16°F | Nov 3 | Nov 7 | Nov 9 | Nov 12 | Nov 14 | Nov 17 | Nov 21 | Nov 25 | Nov 30 |
Freeze probabilities 1991–2020 at Humboldt Wtp, 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 50548 →Compare Humboldt with another place →
Weather by month in Humboldt
July is the warmest month at Humboldt Wtp, IA, averaging 81°F by day and 63°F at night; January is the coldest at 24°F and 9°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 34% of years.
Warmth for growing adds up to 2,705 growing degree days a year (base 50°F), fewer than at 85% of the 132 Iowa stations. 34% of them (923) have built up by the end of June, and July adds the most, 685.
| Month | High °F | Low °F | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|
| Jan | 24 | 9 | 100% | 31 | 0 |
| Feb | 29 | 12 | 100% | 27 | 0 |
| Mar | 43 | 25 | 100% | 25 | 12 |
| Apr | 57 | 36 | 100% | 9 | 72 |
| May | 68 | 49 | 34% | 1 | 283 |
| Jun | 78 | 59 | 0% | 0 | 556 |
| Jul | 81 | 63 | 0% | 0 | 685 |
| Aug | 79 | 60 | 0% | 0 | 604 |
| Sep | 73 | 51 | 23% | <1 | 364 |
| Oct | 60 | 39 | 97% | 8 | 117 |
| Nov | 43 | 26 | 100% | 22 | 11 |
| Dec | 30 | 15 | 100% | 30 | 0 |
Monthly normals 1991–2020 at Humboldt Wtp, IA (1,100 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, Fort Dodge 5NNW, IA, 10 miles south of Humboldt, has a last frost 1 day later (April 28), a first frost 1 day earlier (October 8), a season 4 days shorter.
When it snows in Humboldt, Iowa
The first measurable snow (0.1 inch or more) in Humboldt usually arrives around November 14, and the last of the season around April 8. Those are the middle dates across the winters of 1991–2020 at Fort Dodge 5NNW, IA, 9.5 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 19 days after the last snow.
Planting calendar for 50548
| When | What to do |
|---|---|
| February 16 – March 2 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 2 – March 16 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| March 30 – April 13 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| April 27 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 17 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 25 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 9 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 50548 is under a mile from Humboldt Wtp, IA, which stands at 1,100 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 50548 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.