Fall in zone 5bPhoto: Dietmar Rabich, CC BY-SA 4.0, via Wikimedia Commons
Frost dates for ZIP 52231 (Harper, IA)
Average last spring and first fall frost dates with 10%, 50% and 90% odds, from NOAA's 1991–2020 climate normals for the nearest weather station, Sigourney, IA (9 miles away).
- Average last spring frostApr 2450% chance of a 32°F freeze after this date
- Average first fall frostOct 1550% chance of a 32°F freeze by this date
- Growing season (frost-free)172 daysmedian, 32°F threshold
- USDA hardiness zone5b-15 to -10°F avg. coldest night
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Frost and freeze alerts from the NWS forecast for 52231, the spring soil-temperature heads-up for pre-emergent, and a short weekly yard-timing email.
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This week in your yard
As of Oct 18, 2026, from your frost dates, zone and soil temperature. Lawn timing · Vegetables · Pruning · Plants
Soil temperature now
2-inch depth
No soil station with a fresh reading within 62 miles.
4-inch depth
No soil station with a fresh reading within 62 miles.
Fall: Texas A&M AgriLife times fall pre-emergent (for winter weeds such as annual bluegrass) to soil cooling to about 70°F for several days. The 50–55°F band is the spring trigger. Always read and follow the product label.
7-day forecast and frost risk
The latest National Weather Service 7-day forecast and any Frost Advisory or Freeze Warning for 52231 load here. You can also open the NWS forecast for this ZIP.
Pre-emergent
No soil reading near this ZIP. Typical extension timing for your region: spring mid-April to early May.
Fertilizer window
Lawn region: North (cool-season). Timing only; always follow the product label.
- Kentucky bluegrass (cool-season): Early fall: Around Labor Day (late August–September); Late fall: Late October–November, before the ground freezes; Late spring: Optional around Memorial Day. Avoid: Early-spring and midsummer feeding (pushes top growth, favors crabgrass).
Plant now
No vegetable planting windows are open this week.
Prune now
No frost-timed pruning windows are open this week.
Spring-flowering shrubs are pruned right after their flowers fade, not by date. See the pruning guide.
Last spring frost odds
| Chance of a 32°F freeze after this date | Date |
|---|---|
| 90% (early: most years still freeze after this) | Apr 9 |
| 50% (the "average" last frost) | Apr 24 |
| 10% (cautious: only 1 year in 10 freezes later) | May 9 |
Most gardeners plant frost-tender crops (tomatoes, peppers, basil) after the 50% date, and closer to the 10% date for less risk.
First fall frost odds
| Chance the first 32°F freeze has happened by this date | Date |
|---|---|
| 10% (early: 1 year in 10 freezes this soon) | Sep 30 |
| 50% (the "average" first frost) | Oct 15 |
| 90% (late: most years have frozen by now) | Oct 27 |
Light frost, freeze and hard freeze
| Threshold | Last spring (50%) | First fall (50%) |
|---|---|---|
| 36°F (light frost possible on clear, calm nights) | May 4 | Oct 5 |
| 32°F (freeze) | Apr 24 | Oct 15 |
| 28°F (hard freeze) | Apr 12 | Oct 24 |
n/a means NOAA did not publish a date at that threshold for this station (usually because it rarely gets that cold).
Vegetable planting calendar for 52231
Dates count from your average last spring frost (Apr 24) and first fall frost (Oct 15). Half of years have a frost after the spring date, so give tender crops (tomatoes, peppers, squash) some slack.
| Crop | Start indoors | Spring planting | Fall planting |
|---|---|---|---|
| Tomato | Feb 27–Mar 13 | May 1–15 (transplant) | – |
| Pepper (sweet and hot) | Feb 13–27 | May 8–22 (transplant) | – |
| Eggplant | Feb 13–27 | May 8–22 (transplant) | – |
| Tomatillo | Feb 27–Mar 13 | May 1–15 (transplant) | – |
| Lettuce | Feb 27–Mar 13 | Apr 3–24 (transplant) Mar 27–May 8 (sow outdoors) | Aug 20–Sep 10 (transplant) Aug 6–Sep 3 (sowing) |
| Spinach | – | Mar 13–Apr 3 (sow outdoors) | Aug 20–Sep 10 (sowing) |
| Kale | Feb 27–Mar 13 | Mar 27–Apr 10 (transplant) Mar 27–Apr 10 (sow outdoors) | Jul 23–Aug 20 (transplant) Jul 9–Aug 6 (sowing) |
| Collards | Feb 27–Mar 13 | Mar 27–Apr 24 (transplant) Mar 27–Apr 24 (sow outdoors) | Jul 23–Aug 20 (transplant) Jul 9–Aug 6 (sowing) |
| Broccoli | Feb 13–27 | Mar 27–Apr 10 (transplant) | Jul 9–Aug 6 (transplant) |
| Cabbage | Feb 13–27 | Mar 27–Apr 10 (transplant) | Jul 9–Aug 6 (transplant) |
| Cauliflower | Feb 13–27 | Apr 10–24 (transplant) | Jul 9–Aug 6 (transplant) |
| Brussels sprouts | Jan 30–Feb 13 | Mar 27–Apr 10 (transplant) | Jun 25–Jul 16 (transplant) |
| Kohlrabi | Feb 27–Mar 13 | Mar 27–Apr 10 (transplant) Mar 27–Apr 10 (sow outdoors) | Aug 6–20 (sowing) |
| Bok choy / Asian greens | – | Mar 27–Apr 10 (sow outdoors) | Aug 20–Sep 3 (sowing) |
| Arugula | – | Mar 27–Apr 24 (sow outdoors) | Aug 20–Sep 17 (sowing) |
| Mustard greens | – | Mar 27–Apr 17 (sow outdoors) | Aug 20–Sep 3 (sowing) |
| Swiss chard | Mar 13–27 | Apr 10–May 1 (transplant) Apr 10–May 8 (sow outdoors) | Aug 6–20 (sowing) |
| Beet | – | Mar 27–Apr 24 (sow outdoors) | Aug 6–20 (sowing) |
| Carrot | – | Apr 3–May 1 (sow outdoors) | Jul 23–Aug 6 (sowing) |
| Radish | – | Mar 20–May 1 (sow outdoors) | Sep 3–17 (sowing) |
| Turnip | – | Mar 27–Apr 17 (sow outdoors) | Aug 6–20 (sowing) |
| Parsnip | – | Apr 3–24 (sow outdoors) | – |
| Pea (garden, snap, snow) | – | Feb 27–Mar 27 (sow outdoors) | Jul 23–Aug 6 (sowing) |
| Onion (bulbing) | Jan 30–Feb 13 | Mar 13–27 (transplant) | – |
| Green onion / scallion | – | Mar 13–Apr 10 (sow outdoors) | Aug 6–20 (sowing) |
| Leek | Jan 30–Feb 13 | Mar 27–Apr 10 (transplant) | – |
| Garlic | – | – | Sep 3–Oct 1 (sowing) |
| Shallot | – | Mar 13–27 (transplant) | Sep 3–Oct 1 (sowing) |
| Potato | – | Mar 27–Apr 10 (transplant) | Jun 25–Jul 9 (transplant) |
| Sweet potato | – | May 15–29 (transplant) | – |
| Sweet corn | – | May 1–15 (sow outdoors) | – |
| Bean, bush (snap) | – | May 1–15 (sow outdoors) | – |
| Bean, pole | – | May 1–15 (sow outdoors) | – |
| Lima bean | – | May 8–22 (sow outdoors) | – |
| Southern pea (cowpea, black-eyed pea) | – | May 15–Jun 5 (sow outdoors) | – |
| Cucumber | Mar 27–Apr 3 | May 1–15 (transplant) May 1–15 (sow outdoors) | – |
| Summer squash / zucchini | Mar 27–Apr 3 | May 1–15 (transplant) May 1–15 (sow outdoors) | – |
| Winter squash | Mar 27–Apr 3 | May 1–15 (transplant) May 1–15 (sow outdoors) | – |
| Pumpkin | – | May 1–15 (sow outdoors) | – |
| Watermelon | Mar 27–Apr 3 | May 8–22 (transplant) May 8–22 (sow outdoors) | – |
| Cantaloupe / muskmelon | Mar 27–Apr 3 | May 8–22 (transplant) May 8–22 (sow outdoors) | – |
| Okra | Mar 13–27 | May 8–22 (transplant) May 8–22 (sow outdoors) | – |
| Celery | Jan 30–Feb 13 | May 1–8 (transplant) | – |
| Basil | Mar 13–27 | May 1–15 (transplant) May 1–15 (sow outdoors) | – |
| Cilantro | – | Apr 10–May 8 (sow outdoors) | Aug 20–Sep 3 (sowing) |
| Parsley | Feb 13–27 | Apr 10–24 (transplant) Apr 3–24 (sow outdoors) | – |
| Dill | – | Apr 24–May 8 (sow outdoors) | Aug 20–Sep 3 (sowing) |
| Sunflower | – | Apr 24–May 8 (sow outdoors) | – |
| Asparagus (crowns) | – | Mar 27–Apr 10 (transplant) | – |
| Rhubarb (crowns) | – | Mar 27–Apr 10 (transplant) | – |
| Strawberry (plants) | – | Mar 27–Apr 10 (transplant) | Aug 6–Sep 3 (transplant) |
Typical ranges from university extension planting calendars, adjusted to your frost dates. Probabilities, not guarantees. Fall windows that would overlap spring planting are left out, as are fall crops of frost-tender plants where the frost-free season is under 210 days.
Where these numbers come from
Station: Sigourney, IA (NOAA GHCN-Daily ID USC00137678), elevation 732 ft, 8.9 miles from the ZIP's center point. NOAA completeness flag: S (standard, 24+ years).
Nearby stations
| Station | Distance | Last frost (50%) | First frost (50%) |
|---|---|---|---|
| Washington, IA | 19 mi | Apr 28 | Oct 11 |
| Williamsburg 1E, IA | 21 mi | Apr 28 | Oct 9 |
| Fairfield, IA | 24 mi | Apr 27 | Oct 12 |
The average last-frost dates of these stations span 4 days, a rough guide to local variation. See data sources & methods.
Frost questions for 52231
When is the last frost in 52231?
The average (50% chance) last spring freeze of 32°F for ZIP 52231 is April 24. For a more cautious planting date, use May 9, when only 1 year in 10 still sees a later freeze.
When is the first frost in 52231?
The average first fall freeze is October 15. In 1 year in 10 it comes by September 30.
What hardiness zone is 52231?
ZIP 52231 is in USDA zone 5b (-15 to -10°F average coldest winter night), per the 2023 USDA Plant Hardiness Zone Map ZIP listing.
What is the soil temperature in 52231 right now?
This page shows the latest 2-inch and 4-inch soil temperature from the nearest public soil station (USDA SCAN, NOAA USCRN or TexMesonet), or a labeled estimate when no station is close, against the 50–55°F spring pre-emergent band.
Nearby ZIP codes
52248 Keota 52591 Sigourney 52335 South English 52355 Webster 52576 Ollie 52562 Hayesville 52585 Richland 52359 West Chester
Other ZIP codes in Keokuk County
50104 50136 50255 50268 52335 52355 52550 52562 52563 52568 52576 52585 52591 All Keokuk County frost dates · Iowa frost dates
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Weekly yard timing, plus frost and soil-temperature alerts for your ZIP code.
- Freeze alerts
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Free. One weekly email plus alerts when your ZIP has a frost or a soil-temperature change worth acting on. After you submit, Kit (our email provider) sends a confirmation email: check your email and click the link to confirm. You aren't subscribed until you do. We collect only your email address and ZIP, sent to Kit to deliver The Dial. Unsubscribe anytime.