USDA Hardiness Zone 5a
Frost Dates for 51241 — Larchwood, Iowa
NOAA 1991–2020 normals from Canton, SD (1,316 ft), 12 miles southwest.
Updated
In Larchwood, the last spring frost (32°F) is around May 2 in half of years and has passed by May 15 in nine years out of ten. The first fall frost comes around October 2, as early as September 19 one year in ten, leaving a typical freeze-free season of 151 days (NOAA, Canton, SD).
- Last spring frost
- May 2
- First fall frost
- October 2
- 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 14
- Last snow
- April 3
- Winters with snow
- 100%
- Snow per year
- 36.1"
median, 1991–2020
median, 1991–2020
26 of 26 observed
NOAA normal
Frost risk by date in Larchwood
Half of springs at Canton, SD see their last 32°F night by May 2; only one in ten is past it by April 19, and one in ten still has one after May 15. Planting tender crops after May 7 leaves a 30% risk of a frost on them, after May 10 20%, and after May 15 10%. The 13 days between the even-odds date and the one-in-ten date is narrower than at 42% of the 132 Iowa stations behind this site's ZIP pages.
In fall the first 32°F night comes by October 2 in half of years, as early as September 19 one year in ten, and holds off past October 16 one year in ten. A hard freeze of 28°F follows 9 days later, around October 11; in spring the one-in-ten date for 28°F is May 6, 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 170 days one year in ten and falls short of 133 one year in ten. On average 160 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 May 12, and return around September 25. Severe cold of 16°F or below comes every winter, usually between November 7 and March 30.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 30 | May 3 | May 7 | May 10 | May 12 | May 14 | May 17 | May 20 | May 25 |
| 32°F | Apr 19 | Apr 24 | Apr 27 | Apr 30 | May 2 | May 4 | May 7 | May 10 | May 15 |
| 28°F | Apr 9 | Apr 14 | Apr 17 | Apr 20 | Apr 23 | Apr 26 | Apr 29 | May 1 | May 6 |
| 24°F | Mar 31 | Apr 4 | Apr 7 | Apr 11 | Apr 13 | Apr 17 | Apr 20 | Apr 24 | Apr 29 |
| 20°F | Mar 19 | Mar 26 | Mar 31 | Apr 3 | Apr 5 | Apr 8 | Apr 11 | Apr 15 | Apr 19 |
| 16°F | Mar 11 | Mar 16 | Mar 21 | Mar 25 | Mar 30 | Apr 1 | Apr 4 | Apr 7 | Apr 12 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 12 | Sep 16 | Sep 19 | Sep 22 | Sep 25 | Sep 27 | Sep 30 | Oct 3 | Oct 7 |
| 32°F | Sep 19 | Sep 23 | Sep 26 | Sep 29 | Oct 2 | Oct 4 | Oct 7 | Oct 11 | Oct 16 |
| 28°F | Sep 27 | Oct 2 | Oct 4 | Oct 8 | Oct 11 | Oct 14 | Oct 17 | Oct 21 | Oct 25 |
| 24°F | Oct 4 | Oct 11 | Oct 15 | Oct 19 | Oct 21 | Oct 24 | Oct 26 | Oct 30 | Nov 3 |
| 20°F | Oct 16 | Oct 21 | Oct 25 | Oct 28 | Oct 31 | Nov 2 | Nov 5 | Nov 8 | Nov 13 |
| 16°F | Oct 26 | Oct 30 | Nov 2 | Nov 5 | Nov 7 | Nov 10 | Nov 13 | Nov 17 | Nov 22 |
Freeze probabilities 1991–2020 at Canton, SD, 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 51241 →Compare Larchwood with another place →
Weather by month in Larchwood
July is the warmest month at Canton, SD, averaging 83°F by day and 62°F at night; January is the coldest at 25°F and 6°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 55% of years.
Warmth for growing adds up to 2,727 growing degree days a year (base 50°F), fewer than at 84% of the 132 Iowa stations. 35% of them (942) have built up by the end of June, and July adds the most, 699. Precipitation totals 28.1 inches a year, most in June (4.7") and least in January (0.6"); May to September bring 65% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 25 | 6 | 0.6 | 100% | 31 | 0 |
| Feb | 31 | 11 | 0.8 | 100% | 27 | 1 |
| Mar | 44 | 22 | 1.3 | 100% | 24 | 14 |
| Apr | 58 | 34 | 2.9 | 100% | 12 | 73 |
| May | 70 | 47 | 4.1 | 55% | 1 | 284 |
| Jun | 80 | 58 | 4.7 | 0% | 0 | 570 |
| Jul | 83 | 62 | 3.6 | 0% | 0 | 699 |
| Aug | 80 | 59 | 3.0 | 0% | 0 | 608 |
| Sep | 74 | 50 | 2.9 | 44% | 1 | 368 |
| Oct | 60 | 36 | 2.2 | 100% | 10 | 101 |
| Nov | 44 | 23 | 1.2 | 100% | 24 | 9 |
| Dec | 29 | 11 | 0.8 | 100% | 30 | 0 |
Monthly normals 1991–2020 at Canton, SD (1,316 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, Rock Rapids, IA, 14 miles east of Larchwood, has a last frost 1 day earlier (May 1), a first frost 2 days later (October 4), a season 5 days longer.
When it snows in Larchwood, Iowa
The first measurable snow (0.1 inch or more) in Larchwood usually arrives around November 14, and the last of the season around April 3. Those are the middle dates across the winters of 1991–2020 at Canton, SD, 12.1 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 29 days after the last snow.
Planting calendar for 51241
| When | What to do |
|---|---|
| February 21 – March 7 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 7 – March 21 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| April 4 – April 18 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| May 2 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 10 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 18 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 2 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 51241 is 12 miles from Canton, SD, which stands at 1,316 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 3 other ZIP codes share the station; its figures are presented in full for 57032 (Harrisburg). The 2023 USDA Plant Hardiness Zone Map lists ZIP 51241 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.