Superior, IA frost dates
Last spring frostApr 28median date
First fall frostOct 11median date
Growing season166 daysfrost-free
Hardiness zone5aZone 5a
How Superior compares
- In 8 years out of 10, the last spring frost in Superior falls between April 14 and May 9, a 25-day window. The first fall frost falls between September 27 and October 24.
- The median last frost is the same as the Iowa median of Apr 28.
- Its 166-day growing season is longer than 52% of the 934 Iowa places with a regular frost season (state median 165 days).
- The last frost is 5 days earlier than the zone 5a median of May 3. Hardiness zones measure winter cold, not season length, so use these dates rather than a zone 5a chart.
- The weather station records an average of 149 nights a year at or below 32°F.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | April 14 |
| 50% (median) | April 28 |
| 10% (safe for tender plants) | May 9 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 27 |
| 50% (median) | October 11 |
| 90% (late) | October 24 |
Frost here means 32°F (0°C). A median date means half of years have their last frost earlier and half later.
Planting calendar for Superior, IA
Superior, IA frost dates — last frost Apr 28, first frost Oct 11, zone 5a. whenisthelastfrost.com
Crop
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Start indoors: Feb 3 to Feb 17Transplant outside: Mar 31 to Apr 14
Start indoors: Feb 17 to Mar 3Transplant outside: May 12 to May 26
Start indoors: Feb 17 to Mar 3Transplant outside: May 12 to May 26
Start indoors: Mar 3 to Mar 17Transplant outside: May 5 to May 19
Start indoors: Mar 3 to Mar 17Transplant outside: Apr 7 to Apr 21Sow outdoors: Mar 31 to May 5Plant for fall: Aug 16 to Sep 13
Start indoors: Mar 3 to Mar 17Transplant outside: Mar 31 to Apr 14Sow outdoors: Mar 31 to Apr 14Plant for fall: Aug 2 to Aug 23
Start indoors: Mar 3 to Mar 17Transplant outside: Apr 14 to Apr 28Plant for fall: Jul 5 to Jul 26
Start indoors: Mar 3 to Mar 17Transplant outside: Apr 7 to Apr 21Plant for fall: Jul 5 to Jul 26
Start indoors: Mar 3 to Mar 17Transplant outside: Apr 14 to Apr 28Plant for fall: Jul 5 to Jul 26
Start indoors: Mar 17 to Mar 31Transplant outside: May 19 to Jun 2Sow outdoors: May 19 to Jun 2
Start indoors: Mar 17 to Mar 31Transplant outside: May 5 to May 19
Sow outdoors: Mar 17 to Apr 7Plant for fall: Jul 19 to Aug 9
Sow outdoors: Mar 17 to Apr 7Plant for fall: Aug 16 to Sep 6
Sow outdoors: Mar 24 to May 5Plant for fall: Aug 30 to Sep 20
Start indoors: Mar 31 to Apr 7Transplant outside: May 12 to May 19Sow outdoors: May 5 to May 19Plant for fall: Jul 26 to Aug 9
Start indoors: Mar 31 to Apr 7Sow outdoors: May 5 to May 19Plant for fall: Aug 2 to Aug 16
Start indoors: Mar 31 to Apr 7Sow outdoors: May 5 to May 19
Start indoors: Mar 31 to Apr 7Transplant outside: May 12 to May 26
Sow outdoors: Apr 7 to May 5Plant for fall: Jul 19 to Aug 2
Sow outdoors: Apr 7 to May 5Plant for fall: Aug 2 to Aug 16
Sow outdoors: Apr 7 to Apr 28
Sow outdoors: Apr 14 to May 12Plant for fall: Aug 2 to Aug 16
Sow outdoors: Apr 14 to May 5Plant for fall: Aug 16 to Sep 6
Sow outdoors: May 5 to May 26Plant for fall: Jul 26 to Aug 9
Sow outdoors: May 5 to May 19
Transplant outside: May 12 to Jun 2
Plant for fall: Sep 27 to Nov 1
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Superior, IA
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Feb 3 – Feb 17 | Mar 31 – Apr 14 | — | — |
| Peppers | Feb 17 – Mar 3 | May 12 – May 26 | — | — |
| Eggplant | Feb 17 – Mar 3 | May 12 – May 26 | — | — |
| Tomatoes | Mar 3 – Mar 17 | May 5 – May 19 | — | — |
| Lettuce | Mar 3 – Mar 17 | Apr 7 – Apr 21 | Mar 31 – May 5 | Aug 16 – Sep 13 |
| Kale | Mar 3 – Mar 17 | Mar 31 – Apr 14 | Mar 31 – Apr 14 | Aug 2 – Aug 23 |
| Broccoli | Mar 3 – Mar 17 | Apr 14 – Apr 28 | — | Jul 5 – Jul 26 |
| Cabbage | Mar 3 – Mar 17 | Apr 7 – Apr 21 | — | Jul 5 – Jul 26 |
| Cauliflower | Mar 3 – Mar 17 | Apr 14 – Apr 28 | — | Jul 5 – Jul 26 |
| Okra | Mar 17 – Mar 31 | May 19 – Jun 2 | May 19 – Jun 2 | — |
| Basil | Mar 17 – Mar 31 | May 5 – May 19 | — | — |
| Peas | — | — | Mar 17 – Apr 7 | Jul 19 – Aug 9 |
| Spinach | — | — | Mar 17 – Apr 7 | Aug 16 – Sep 6 |
| Radishes | — | — | Mar 24 – May 5 | Aug 30 – Sep 20 |
| Cucumbers | Mar 31 – Apr 7 | May 12 – May 19 | May 5 – May 19 | Jul 26 – Aug 9 |
| Zucchini & Summer Squash | Mar 31 – Apr 7 | — | May 5 – May 19 | Aug 2 – Aug 16 |
| Winter Squash & Pumpkins | Mar 31 – Apr 7 | — | May 5 – May 19 | — |
| Melons & Watermelon | Mar 31 – Apr 7 | May 12 – May 26 | — | — |
| Carrots | — | — | Apr 7 – May 5 | Jul 19 – Aug 2 |
| Beets | — | — | Apr 7 – May 5 | Aug 2 – Aug 16 |
| Potatoes | — | — | Apr 7 – Apr 28 | — |
| Swiss Chard | — | — | Apr 14 – May 12 | Aug 2 – Aug 16 |
| Cilantro | — | — | Apr 14 – May 5 | Aug 16 – Sep 6 |
| Green Beans | — | — | May 5 – May 26 | Jul 26 – Aug 9 |
| Sweet Corn | — | — | May 5 – May 19 | — |
| Sweet Potatoes | — | May 12 – Jun 2 | — | — |
| Garlic | — | — | — | Sep 27 – Nov 1 |
Dates come from the median frost dates and common extension-service timing. Adjust for your soil temperature, microclimate and the varieties you grow.
About these dates
Based on 1991–2020 NOAA climate normals for the Spirit Lake, IA weather station, 16 km away (elevation 1,421 ft (433 m)).
Frost dates near Superior
- Estherville May 2 · Oct 3
- Terril Apr 28 · Oct 11
- Spirit Lake Apr 28 · Oct 11
- Okoboji Apr 28 · Oct 11
- Arnolds Park May 1 · Oct 6
- Wallingford May 2 · Oct 3
- Milford May 1 · Oct 6
- Dolliver May 2 · Sep 30
- Graettinger Apr 27 · Oct 7
- Lake Park Apr 30 · Oct 10
Frequently asked questions
When is the last frost in Superior, IA?
The median last spring frost in Superior, IA is April 28. There is still about a 10% chance of frost after May 9, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Superior, IA?
The median first fall frost is October 11, with about a 10% chance of frost before September 27.
How long is the growing season in Superior, IA?
About 166 days between the median last spring frost and first fall frost.
What planting zone is Superior, IA?
Superior, IA is in USDA hardiness zone 5a.