USDA Hardiness Zone 5b
Frost Dates for 50219 — Pella, Iowa
NOAA 1991–2020 normals from Knoxville, IA (895 ft), 12 miles southwest.
Updated
In Pella, the last spring frost (32°F) is around April 20 in half of years and has passed by May 4 in nine years out of ten. The first fall frost comes around October 19, as early as October 1 one year in ten, leaving a typical freeze-free season of 180 days (NOAA, Knoxville, IA).
- Last spring frost
- April 20
- First fall frost
- October 19
- Growing season
- 180 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 25
- Last snow
- March 19
- Winters with snow
- 100%
- Snow per year
- —
median, 1991–2020
median, 1991–2020
30 of 30 observed
NOAA normal
Frost risk by date in Pella
Half of springs at Knoxville, IA see their last 32°F night by April 20; only one in ten is past it by April 6, and one in ten still has one after May 4. Planting tender crops after April 26 leaves a 30% risk of a frost on them, after April 30 20%, and after May 4 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 19 in half of years, as early as October 1 one year in ten, and holds off past November 1 one year in ten. A hard freeze of 28°F follows 10 days later, around October 29; in spring the one-in-ten date for 28°F is April 24, 10 days before the 32°F one. The freeze-free season lasts 180 days in a typical year, longer than at 87% of the 132 Iowa stations; it reaches 199 days one year in ten and falls short of 159 one year in ten. On average 133 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 10 days longer, to about April 30, and return around October 7. Severe cold of 16°F or below comes every winter, usually between November 24 and March 14.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 15 | Apr 20 | Apr 24 | Apr 28 | Apr 30 | May 3 | May 6 | May 8 | May 12 |
| 32°F | Apr 6 | Apr 10 | Apr 14 | Apr 17 | Apr 20 | Apr 23 | Apr 26 | Apr 30 | May 4 |
| 28°F | Mar 28 | Apr 2 | Apr 5 | Apr 7 | Apr 10 | Apr 12 | Apr 16 | Apr 19 | Apr 24 |
| 24°F | Mar 15 | Mar 22 | Mar 27 | Mar 31 | Apr 2 | Apr 4 | Apr 7 | Apr 10 | Apr 16 |
| 20°F | Mar 6 | Mar 11 | Mar 16 | Mar 20 | Mar 24 | Mar 28 | Mar 31 | Apr 3 | Apr 7 |
| 16°F | Feb 28 | Mar 4 | Mar 8 | Mar 11 | Mar 14 | Mar 17 | Mar 21 | Mar 26 | Mar 31 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 23 | Sep 29 | Oct 1 | Oct 5 | Oct 7 | Oct 10 | Oct 13 | Oct 17 | Oct 21 |
| 32°F | Oct 1 | Oct 8 | Oct 13 | Oct 15 | Oct 19 | Oct 22 | Oct 24 | Oct 27 | Nov 1 |
| 28°F | Oct 14 | Oct 20 | Oct 23 | Oct 26 | Oct 29 | Nov 1 | Nov 2 | Nov 5 | Nov 9 |
| 24°F | Oct 23 | Oct 29 | Nov 1 | Nov 3 | Nov 5 | Nov 8 | Nov 10 | Nov 15 | Nov 20 |
| 20°F | Nov 1 | Nov 4 | Nov 7 | Nov 10 | Nov 14 | Nov 18 | Nov 21 | Nov 25 | Dec 1 |
| 16°F | Nov 7 | Nov 12 | Nov 17 | Nov 20 | Nov 24 | Nov 27 | Dec 1 | Dec 4 | Dec 10 |
Freeze probabilities 1991–2020 at Knoxville, 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 50219 →Compare Pella with another place →
Frost risk through the year in Pella
In Pella, the spring curve drops under 10% on May 4 and the fall curve passes 10% on October 1, 150 days later; that gap is longer than at 83% of the 132 Iowa stations with frost dates. The spring risk falls from 90% to 10% over 28 days (April 6 to May 4) and the fall risk climbs from 10% to 90% over 31 days (October 1 to November 1): both ends of the season vary about as much. At Oskaloosa, IA, 15 miles southeast, the same gap runs from May 4 to September 29, 2 days shorter.
| Planted on | Another 32°F night | 28°F night |
|---|---|---|
| Apr 6 | over 90% | 65% |
| Apr 13 | 73% | 38% |
| Apr 2050% date | 50% | 18% |
| Apr 27 | 28% | under 10% |
| May 4 | under 10% | under 10% |
| May 11 | under 10% | under 10% |
Weather by month in Pella
July is the warmest month at Knoxville, IA, averaging 85°F by day and 66°F at night; January is the coldest at 30°F and 13°F. A freezing night is all but certain in every month from November to April (a 90% chance or more). From June to September the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 19% of years.
Warmth for growing adds up to 3,279 growing degree days a year (base 50°F), more than at 82% of the 132 Iowa stations. 35% of them (1,134) have built up by the end of June, and July adds the most, 778. Precipitation totals 37.7 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 | 30 | 13 | 1.2 | 100% | 30 | 0 |
| Feb | 35 | 17 | 1.7 | 100% | 25 | 3 |
| Mar | 48 | 28 | 1.9 | 100% | 21 | 30 |
| Apr | 61 | 39 | 3.9 | 96% | 7 | 120 |
| May | 71 | 51 | 5.0 | 19% | <1 | 353 |
| Jun | 81 | 61 | 5.6 | 0% | 0 | 628 |
| Jul | 85 | 66 | 4.3 | 0% | 0 | 778 |
| Aug | 83 | 63 | 3.9 | 0% | 0 | 710 |
| Sep | 76 | 54 | 3.7 | 8% | <1 | 461 |
| Oct | 63 | 42 | 3.1 | 88% | 5 | 168 |
| Nov | 48 | 30 | 1.8 | 100% | 18 | 28 |
| Dec | 36 | 19 | 1.6 | 100% | 28 | 1 |
Monthly normals 1991–2020 at Knoxville, IA (895 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, Oskaloosa, IA, 15 miles southeast of Pella, has a last frost 1 day later (April 21), a first frost 3 days earlier (October 16), a season 4 days shorter.
When it snows in Pella, Iowa
The first measurable snow (0.1 inch or more) in Pella usually arrives around November 25, and the last of the season around March 19. Those are the middle dates across the winters of 1991–2020 at Pella 1S, IA, 2.5 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 32 days after the last snow.
Planting calendar for 50219
| When | What to do |
|---|---|
| February 9 – February 23 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| February 23 – March 9 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| March 23 – April 6 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| April 20 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 27 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by October 5 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 19 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 50219 is 12 miles from Knoxville, IA, which stands at 895 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 2 other ZIP codes share the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 50219 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.