Oskaloosa, IA planting zone & frost dates
Oskaloosa is in USDA hardiness zone 5b. The last spring frost usually comes around April 21 and the first fall frost around October 16, for a growing season of about 176 days.
Planting calendar for Oskaloosa
Dates are counted from the average last spring frost (April 21) using the typical timing recommended by U.S. extension services. Warm-season crops go out only after the danger of frost has passed and the soil has warmed.
| Crop | When |
|---|---|
| Tomatoes | Start seeds indoors: Feb 24 – Mar 10 Transplant outdoors: Apr 28 – May 5 |
| Peppers | Start seeds indoors: Feb 10 – Feb 24 Transplant outdoors: May 5 – May 12 |
| Eggplant | Start seeds indoors: Feb 10 – Feb 24 Transplant outdoors: May 5 – May 12 |
| Broccoli | Start seeds indoors: Feb 10 – Feb 24 Transplant outdoors: Mar 24 – Apr 7 |
| Cabbage | Start seeds indoors: Feb 10 – Feb 24 Transplant outdoors: Mar 24 – Apr 7 |
| Onions (sets) | Plant outdoors: Mar 24 – Apr 7 |
| Peas | Sow outdoors: Mar 10 – Mar 24 |
| Spinach | Sow outdoors: Mar 10 – Mar 24 |
| Lettuce | Sow outdoors: Mar 24 – Apr 7 |
| Carrots | Sow outdoors: Mar 24 – Apr 7 |
| Potatoes | Plant outdoors: Mar 24 – Apr 7 |
| Beans | Sow outdoors: Apr 28 – May 5 |
| Sweet corn | Sow outdoors: Apr 28 – May 5 |
| Cucumbers | Sow outdoors: Apr 28 – May 5 |
| Squash & zucchini | Sow outdoors: Apr 28 – May 5 |
| Basil | Start seeds indoors: Mar 10 – Mar 24 Transplant outdoors: Apr 28 – May 5 |
Fall garden: cool-season crops like lettuce, spinach and kale can be sown again around Aug 21 (8 weeks before the average first fall frost on Oct 16).
Useful for zone 5b gardens
- Seed starting kit with dome — to start seeds indoors before the last frost
- LED grow light for seedlings — stops leggy seedlings
- Frost cloth / plant covers — for late spring and early fall frosts
- Soil thermometer — warm-season crops need soil above 60°F
- Cold frame / mini greenhouse — adds weeks to a short season
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Frost risk in detail
| 90% chance | 50% chance | 10% chance | |
|---|---|---|---|
| Last 32°F frost in spring is after | Apr 8 | Apr 21 | May 4 |
| First 32°F frost in fall is before | Oct 29 | Oct 16 | Sep 29 |
How to read it: in spring there is a 10% chance of a frost after May 4, so that is a safe date for tender plants. In fall there is a 10% chance of frost before September 29. A hard freeze (28°F) usually ends around April 11.
Hardiness zone by ZIP code in Oskaloosa
- 52577 zone 5b
Nearby cities
- Pella zone 5b, last frost Apr 20
- Ottumwa zone 5b, last frost Apr 23
- Newton zone 5b, last frost Apr 22
- Marshalltown zone 5a, last frost Apr 28
- Altoona zone 5b, last frost Apr 21
- Indianola zone 5b, last frost Apr 24
- Des Moines zone 5b, last frost Apr 18
- Norwalk zone 5b, last frost Apr 18
Questions
What growing zone is Oskaloosa, IA?
Oskaloosa is in USDA Plant Hardiness Zone 5b (average extreme winter low -15°F to -10°F), according to the USDA 2023 map.
When is the last frost in Oskaloosa?
The average last spring frost (32°F) in Oskaloosa is April 21. There is still a 10% chance of frost until May 4.
When can I plant tomatoes in Oskaloosa?
Transplant tomatoes outdoors 1–2 weeks after the average last frost: around Apr 28 – May 5. Start seeds indoors 6–8 weeks before the last frost.
Frost dates: NOAA U.S. Climate Normals 1991–2020, station Oskaloosa, IA (USC00136327), 2.8 km (1.7 mi) from the city center, elevation 253 m, based on 26 years of records. Hardiness zone: USDA Plant Hardiness Zone Map 2023 for the ZIP code nearest to the city center. Microclimates (valleys, hills, cities, coasts) can be warmer or colder: check the local forecast before planting. How we calculate the data.