Sioux City, Iowa: planting zone & frost dates
Sioux City is in USDA plant hardiness zone 5a, where the average coldest winter night reaches -20 to -15°F (-28.9 to -26.1°C). The typical last spring frost is around May 4 and the first fall frost around Oct 1.
Frost dates
| Probability | Last spring frost (32°F) | First fall frost (32°F) |
|---|---|---|
| Safer (10% risk) | May 11 | Sep 24 |
| Typical planning date (30% risk) | May 4 | Oct 1 |
| Median (50%) | Apr 29 | Oct 7 |
How to read this: after the spring "10% risk" date, a 32°F frost happens in only about 1 year in 10. In fall, the "10% risk" date is the early end — a frost before it happens about 1 year in 10.
Frost data comes from NOAA station SIOUX CITY ANG, IA (USC00137702), 6.8 mi (11.0 km) from the city center and 13 ft higher than the city center (+4 m). Record used for the 1991–2020 normals: 10 years.
Why your yard may differ from the station: microclimates.
Hardiness zone across Sioux City
All 9 ZIP codes covering Sioux City are in zone 5a.
Vegetable planting calendar for Sioux City
Dates are counted from the 30%-risk frost dates above (last frost May 4, first frost Oct 1). Shift a week later in cold spots or low-lying ground.
| Crop | Start indoors | Transplant / plant out | Direct sow | Fall crop sow/plant |
|---|---|---|---|---|
| Tomato | Mar 9 – Mar 23 | May 11 – May 25 | — | — |
| Pepper | Feb 23 – Mar 9 | May 18 – Jun 1 | — | — |
| Lettuce | Mar 23 – Apr 6 | Apr 20 – May 11 | Apr 6 – May 18 | Jul 23 – Aug 20 |
| Green Beans | — | — | May 11 – Jun 15 | Jul 9 – Jul 23 |
| Sweet Corn | — | — | May 11 – Jun 8 | — |
| Zucchini & Summer Squash | Apr 6 – Apr 13 | May 11 – May 25 | May 11 – Jun 1 | Jul 9 – Jul 23 |
| Cucumber | Apr 6 – Apr 13 | May 18 – May 25 | May 11 – Jun 1 | Jul 9 – Jul 23 |
| Carrot | — | — | Apr 13 – May 18 | Jul 9 – Jul 23 |
| Onion | Feb 9 – Feb 23 | Apr 6 – Apr 20 | — | — |
| Potato | — | Apr 6 – Apr 27 | — | — |
| Basil | Mar 23 – Apr 6 | May 18 – Jun 1 | May 18 – Jun 8 | — |
| Spinach | — | — | Mar 23 – Apr 20 | Aug 6 – Sep 3 |
| Kale | Mar 9 – Mar 23 | Apr 6 – Apr 27 | Apr 6 – Apr 27 | Jul 23 – Aug 20 |
| Broccoli | Mar 9 – Mar 23 | Apr 20 – May 11 | — | Jul 9 – Jul 23 |
| Peas | — | — | Mar 23 – Apr 13 | Jul 23 – Aug 6 |
| Eggplant | Feb 23 – Mar 9 | May 18 – Jun 1 | — | — |
| Cabbage | Mar 9 – Mar 23 | Apr 6 – Apr 20 | — | Jul 9 – Jul 23 |
| Radish | — | — | Mar 30 – May 18 | Aug 20 – Sep 17 |
| Strawberry | — | Apr 6 – Apr 27 | — | — |
| Beets | — | — | Apr 13 – May 25 | Jul 23 – Aug 6 |
Nearby cities in Iowa
- Ankeny — zone 5b, last frost Apr 29, first frost Oct 9
- Des Moines — zone 5b, last frost Apr 24, first frost Oct 14
- Cedar Rapids — zone 5a, last frost May 3, first frost Oct 5
- Iowa City — zone 5b, last frost Apr 28, first frost Oct 13
- Davenport — zone 5b, last frost Apr 24, first frost Oct 17
More: all Iowa cities · other zone 5a cities: Minneapolis, MN, St. Paul, MN, Anchorage, AK, Sioux Falls, SD, Cedar Rapids, IA, Billings, MT, Bloomington, MN, Brooklyn Park, MN
Sioux City gardening questions
When is the last frost in Sioux City, IA?
Plan around May 4. At NOAA's Sioux City Ang, IA station, 6.8 mi from the city center, there is a 30% chance of a 32°F frost after that date. Half of springs have their last frost by Apr 29, and after May 11 the risk drops to about 1 in 10. A hard freeze (28°F) usually ends earlier, around Apr 19. The last frost is fairly predictable here: only 26 days separate the 90% and 10% dates (median for cities on this site: 36 days).
When should I plant tomatoes in Sioux City, IA?
Start seeds indoors Mar 9 – Mar 23 and set transplants outside May 11 – May 25, once nights stay above 50°F and the soil is near 60°F. That leaves 150 days between the 30% frost dates, enough for most varieties including 80–85-day slicers. More: tomato planting dates by zone.
How long is the growing season in Sioux City?
About 161 days without a 32°F frost in a typical (median) year. In 9 years out of 10 the season lasts at least 143 days, and in 1 year in 10 it runs 178 days or more. In fall there is a 10% chance of frost by Sep 24 and a 30% chance by Oct 1. That is the shortest of the 6 Iowa cities on this site.
When should I plant a fall garden in Sioux City?
Count back from the first fall frost (Oct 1): transplant broccoli Jul 9 – Jul 23; sow kale Jul 23 – Aug 20; sow lettuce Jul 23 – Aug 20; sow radishes Aug 20 – Sep 17. Hardy crops keep growing through light frosts; the median 28°F hard freeze here is Oct 18. How the math works: succession and fall planting.
Did Sioux City's hardiness zone change on the 2023 map?
No. Going by the zone that covers most of the city's land, Sioux City is zone 5a on both the 2012 and the 2023 USDA maps (PRISM/OSU ZIP listings). About 42% of U.S. ZIP codes kept their half-zone in 2023. Why the 2023 map is warmer.
How does Sioux City compare with Sioux Falls, SD?
Both are in zone 5a. The typical last spring frost in Sioux City (May 4) comes about the same time as in Sioux Falls, SD (May 6), 74 miles away, and the first fall frost is Oct 1 versus Sep 30. Sioux City sits about 388 ft lower, which explains part of the gap. The two cities use different NOAA stations.