Waterloo, IA planting zone & frost dates
Waterloo is in USDA hardiness zone 5a. The last spring frost usually comes around April 27 and the first fall frost around October 10, for a growing season of about 165 days.
Planting calendar for Waterloo
Dates are counted from the average last spring frost (April 27) 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: Mar 2 – Mar 16 Transplant outdoors: May 4 – May 11 |
| Peppers | Start seeds indoors: Feb 16 – Mar 2 Transplant outdoors: May 11 – May 18 |
| Eggplant | Start seeds indoors: Feb 16 – Mar 2 Transplant outdoors: May 11 – May 18 |
| Broccoli | Start seeds indoors: Feb 16 – Mar 2 Transplant outdoors: Mar 30 – Apr 13 |
| Cabbage | Start seeds indoors: Feb 16 – Mar 2 Transplant outdoors: Mar 30 – Apr 13 |
| Onions (sets) | Plant outdoors: Mar 30 – Apr 13 |
| Peas | Sow outdoors: Mar 16 – Mar 30 |
| Spinach | Sow outdoors: Mar 16 – Mar 30 |
| Lettuce | Sow outdoors: Mar 30 – Apr 13 |
| Carrots | Sow outdoors: Mar 30 – Apr 13 |
| Potatoes | Plant outdoors: Mar 30 – Apr 13 |
| Beans | Sow outdoors: May 4 – May 11 |
| Sweet corn | Sow outdoors: May 4 – May 11 |
| Cucumbers | Sow outdoors: May 4 – May 11 |
| Squash & zucchini | Sow outdoors: May 4 – May 11 |
| Basil | Start seeds indoors: Mar 16 – Mar 30 Transplant outdoors: May 4 – May 11 |
Fall garden: cool-season crops like lettuce, spinach and kale can be sown again around Aug 15 (8 weeks before the average first fall frost on Oct 10).
Useful for zone 5a 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 11 | Apr 27 | May 10 |
| First 32°F frost in fall is before | Oct 21 | Oct 10 | Sep 26 |
How to read it: in spring there is a 10% chance of a frost after May 10, so that is a safe date for tender plants. In fall there is a 10% chance of frost before September 26. A hard freeze (28°F) usually ends around April 16.
Hardiness zone by ZIP code in Waterloo
- 50701 zone 5a
- 50702 zone 5a
- 50703 zone 5a
- 50704 zone 5a
Nearby cities
- Cedar Falls zone 5a, last frost Apr 27
- Waverly zone 5a, last frost Apr 27
- Marshalltown zone 5a, last frost Apr 28
- Cedar Rapids zone 5b, last frost Apr 28
- Marion zone 5a, last frost Apr 28
- North Liberty zone 5b, last frost Apr 21
- Newton zone 5b, last frost Apr 22
- Mason City zone 5a, last frost Apr 29
Questions
What growing zone is Waterloo, IA?
Waterloo is in USDA Plant Hardiness Zone 5a (average extreme winter low -20°F to -15°F), according to the USDA 2023 map.
When is the last frost in Waterloo?
The average last spring frost (32°F) in Waterloo is April 27. There is still a 10% chance of frost until May 10.
When can I plant tomatoes in Waterloo?
Transplant tomatoes outdoors 1–2 weeks after the average last frost: around May 4 – May 11. Start seeds indoors 6–8 weeks before the last frost.
Frost dates: NOAA U.S. Climate Normals 1991–2020, station Waterloo Muni Ap, IA (USW00094910), 8.3 km (5.2 mi) from the city center, elevation 265 m, based on 30 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.