Royal, IA frost dates
Last spring frostMay 2median date
First fall frostOct 2median date
Growing season153 daysfrost-free
Hardiness zone5aZone 5a
How Royal compares
- In 8 years out of 10, the last spring frost in Royal falls between April 17 and May 15, a 28-day window. The first fall frost falls between September 18 and October 16.
- The median last frost is 4 days later than the Iowa median of Apr 28.
- Its 153-day growing season is longer than 6% of the 934 Iowa places with a regular frost season (state median 165 days).
- The last frost is typical for zone 5a, where the median is May 3.
- The weather station records an average of 163 nights a year at or below 32°F.
- Compared with Sioux City, IA, 111 km away, the last frost here is 3 days later than there and the growing season is 8 days shorter.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | April 17 |
| 50% (median) | May 2 |
| 10% (safe for tender plants) | May 15 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 18 |
| 50% (median) | October 2 |
| 90% (late) | October 16 |
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 Royal, IA
Royal, IA frost dates — last frost May 2, first frost Oct 2, zone 5a. whenisthelastfrost.com
Crop
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Start indoors: Feb 7 to Feb 21Transplant outside: Apr 4 to Apr 18
Start indoors: Feb 21 to Mar 7Transplant outside: May 16 to May 30
Start indoors: Feb 21 to Mar 7Transplant outside: May 16 to May 30
Start indoors: Mar 7 to Mar 21Transplant outside: May 9 to May 23
Start indoors: Mar 7 to Mar 21Transplant outside: Apr 11 to Apr 25Sow outdoors: Apr 4 to May 9Plant for fall: Aug 7 to Sep 4
Start indoors: Mar 7 to Mar 21Transplant outside: Apr 4 to Apr 18Sow outdoors: Apr 4 to Apr 18Plant for fall: Jul 24 to Aug 14
Start indoors: Mar 7 to Mar 21Transplant outside: Apr 18 to May 2Plant for fall: Jun 26 to Jul 17
Start indoors: Mar 7 to Mar 21Transplant outside: Apr 11 to Apr 25Plant for fall: Jun 26 to Jul 17
Start indoors: Mar 7 to Mar 21Transplant outside: Apr 18 to May 2Plant for fall: Jun 26 to Jul 17
Start indoors: Mar 21 to Apr 4Transplant outside: May 23 to Jun 6Sow outdoors: May 23 to Jun 6
Start indoors: Mar 21 to Apr 4Transplant outside: May 9 to May 23
Sow outdoors: Mar 21 to Apr 11Plant for fall: Jul 10 to Jul 31
Sow outdoors: Mar 21 to Apr 11Plant for fall: Aug 7 to Aug 28
Sow outdoors: Mar 28 to May 9Plant for fall: Aug 21 to Sep 11
Start indoors: Apr 4 to Apr 11Transplant outside: May 16 to May 23Sow outdoors: May 9 to May 23Plant for fall: Jul 17 to Jul 31
Start indoors: Apr 4 to Apr 11Sow outdoors: May 9 to May 23Plant for fall: Jul 24 to Aug 7
Start indoors: Apr 4 to Apr 11Sow outdoors: May 9 to May 23
Start indoors: Apr 4 to Apr 11Transplant outside: May 16 to May 30
Sow outdoors: Apr 11 to May 9Plant for fall: Jul 10 to Jul 24
Sow outdoors: Apr 11 to May 9Plant for fall: Jul 24 to Aug 7
Sow outdoors: Apr 11 to May 2
Sow outdoors: Apr 18 to May 16Plant for fall: Jul 24 to Aug 7
Sow outdoors: Apr 18 to May 9Plant for fall: Aug 7 to Aug 28
Sow outdoors: May 9 to May 30Plant for fall: Jul 17 to Jul 31
Sow outdoors: May 9 to May 23
Transplant outside: May 16 to Jun 6
Plant for fall: Sep 18 to Oct 23
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Royal, IA
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Feb 7 – Feb 21 | Apr 4 – Apr 18 | — | — |
| Peppers | Feb 21 – Mar 7 | May 16 – May 30 | — | — |
| Eggplant | Feb 21 – Mar 7 | May 16 – May 30 | — | — |
| Tomatoes | Mar 7 – Mar 21 | May 9 – May 23 | — | — |
| Lettuce | Mar 7 – Mar 21 | Apr 11 – Apr 25 | Apr 4 – May 9 | Aug 7 – Sep 4 |
| Kale | Mar 7 – Mar 21 | Apr 4 – Apr 18 | Apr 4 – Apr 18 | Jul 24 – Aug 14 |
| Broccoli | Mar 7 – Mar 21 | Apr 18 – May 2 | — | Jun 26 – Jul 17 |
| Cabbage | Mar 7 – Mar 21 | Apr 11 – Apr 25 | — | Jun 26 – Jul 17 |
| Cauliflower | Mar 7 – Mar 21 | Apr 18 – May 2 | — | Jun 26 – Jul 17 |
| Okra | Mar 21 – Apr 4 | May 23 – Jun 6 | May 23 – Jun 6 | — |
| Basil | Mar 21 – Apr 4 | May 9 – May 23 | — | — |
| Peas | — | — | Mar 21 – Apr 11 | Jul 10 – Jul 31 |
| Spinach | — | — | Mar 21 – Apr 11 | Aug 7 – Aug 28 |
| Radishes | — | — | Mar 28 – May 9 | Aug 21 – Sep 11 |
| Cucumbers | Apr 4 – Apr 11 | May 16 – May 23 | May 9 – May 23 | Jul 17 – Jul 31 |
| Zucchini & Summer Squash | Apr 4 – Apr 11 | — | May 9 – May 23 | Jul 24 – Aug 7 |
| Winter Squash & Pumpkins | Apr 4 – Apr 11 | — | May 9 – May 23 | — |
| Melons & Watermelon | Apr 4 – Apr 11 | May 16 – May 30 | — | — |
| Carrots | — | — | Apr 11 – May 9 | Jul 10 – Jul 24 |
| Beets | — | — | Apr 11 – May 9 | Jul 24 – Aug 7 |
| Potatoes | — | — | Apr 11 – May 2 | — |
| Swiss Chard | — | — | Apr 18 – May 16 | Jul 24 – Aug 7 |
| Cilantro | — | — | Apr 18 – May 9 | Aug 7 – Aug 28 |
| Green Beans | — | — | May 9 – May 30 | Jul 17 – Jul 31 |
| Sweet Corn | — | — | May 9 – May 23 | — |
| Sweet Potatoes | — | May 16 – Jun 6 | — | — |
| Garlic | — | — | — | Sep 18 – Oct 23 |
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 Spencer Muni Ap, IA weather station, 14 km away (elevation 1,339 ft (408 m)).
Frost dates near Royal
- Fostoria May 1 · Oct 3
- Everly May 2 · Oct 2
- Peterson Apr 30 · Oct 5
- Spencer May 1 · Oct 3
- Greenville Apr 30 · Oct 5
- Gillett Grove Apr 30 · Oct 5
- Sutherland Apr 29 · Oct 10
- Sioux Rapids Apr 30 · Oct 5
- Linn Grove Apr 30 · Oct 5
- Hartley May 1 · Oct 7
Frequently asked questions
When is the last frost in Royal, IA?
The median last spring frost in Royal, IA is May 2. There is still about a 10% chance of frost after May 15, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Royal, IA?
The median first fall frost is October 2, with about a 10% chance of frost before September 18.
How long is the growing season in Royal, IA?
About 153 days between the median last spring frost and first fall frost.
What planting zone is Royal, IA?
Royal, IA is in USDA hardiness zone 5a.