Frost dates in Iowa

Across Iowa's 150 NOAA stations with a frost every year, the typical last spring frost ranges from April 10 at Keokuk Lock Dam 19 (530 feet above sea level) to May 8 at Elkader 6 SSW (790 feet above sea level). The middle station's date is April 28.

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Last frost across Iowa

The frost-free season runs from 145 days at Sheldon to 198 days at Keokuk Lock Dam 19.

The station with the latest frost is about 160 miles farther north than the one with the earliest.

These are typical dates: in half of springs the last frost comes later. Each place's page, and each ZIP code lookup, also gives the late-year date, after which only 1 spring in 10 has a frost. That's the safer date for tender plants.

Frost dates for Iowa's larger places

Typical (1-in-2) dates. Each place's page has the early and late years, a planting calendar and a printable planner. Zones are for the ZIP code nearest each place's center.

Hardiness zones in Iowa

Iowa's 1,034 ZIP codes in the USDA list fall in zones 4b to 6a: 4b (2 percent), 5a (54 percent), 5b (41 percent) and 6a (3 percent). Compared with the 2012 map, 24 percent of them moved to a warmer half zone (1 by a full zone or more), 75 percent stayed the same and 3 moved to a colder one.

A hardiness zone is about the coldest night of winter, which decides which shrubs, trees and perennials survive. Frost dates are about spring and fall, which decide when to plant. You need both. Read more about what the zones mean and what changed in 2023.

Every NOAA station in Iowa

All 150 stations in Iowa with frost statistics in NOAA's 1991 to 2020 normals, from A to Z. Station names are usually a town, an airport, or a distance and direction from a town. Find one near you and at a similar elevation.

Typical (1-in-2) dates at 32°F. For the early and late years, and a planting calendar built from your own dates, look up your ZIP code.