Frost dates / Iowa / Marion

Frost dates in Marion, IA

The station on this page is CEDAR RAPIDS #1, IA US (USC00131319), 0.4 miles from the city point. Population in the Census 2024 estimate is 42,542.

Zone 5aUSDA average annual extreme minimum -20°F to -15°F, from ZIP 52302 (1.9 miles from the city point used on this page).

Median last 32°F is April 28. Median first 32°F is October 12. The 50% growing-season length is 166 days. The green band runs from the median last frost to the median first frost. Thin ticks mark the 10%, 50%, and 90% dates.

Outside the median season Growing seasonTicks: 10%, 50%, and 90%

Last 32°F in spring

NCEI’s probability is the chance the last spring minimum of 32°F or lower occurs on or after the date.

Probability	Date	How to read it
90%	April 14	Earlier date. A last 32°F on or after this day is common.
50%	April 28	Median.
10%	May 13	Later date. A last 32°F on or after this day is uncommon.

First 32°F in fall

NCEI’s probability is the chance the first autumn minimum of 32°F or lower occurs on or before the date.

Probability	Date	How to read it
10%	September 29	Earlier date. A first 32°F on or before this day is uncommon.
50%	October 12	Median.
90%	October 25	Later date. A first 32°F on or before this day is common.

32°F growing-season length

Days between the last spring 32°F and the first autumn 32°F. The figure is a length the season meets or exceeds at that probability, from NCEI, not a subtraction done on this site.

Probability the season is at least this long	Days
10%	184
50%	166
90%	144

28°F threshold

	10%	50%	90%
Last, on or after	May 2	April 17	April 4
First, on or before	October 8	October 22	November 1
Season at least	205 days	186 days	166 days

36°F threshold

	10%	50%	90%
Last, on or after	May 22	May 7	April 23
First, on or before	September 19	October 2	October 14
Season at least	166 days	147 days	128 days

Station CEDAR RAPIDS #1, IA US (USC00131319). Completeness flag S, 30 years used for the 32°F dates. NCEI’s annual probability of at least one day at or below 32°F is 100%. Freeze dates are conditional on that threshold occurring. Elevation 247.8 m. The same probability language applies to the 28°F and 36°F rows when those dates passed the same quality checks.

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Marion, IA

Zone 5aAverage annual extreme minimum -20°F to -15°F

Outside the median season Growing seasonTicks: 10%, 50%, and 90%

Iowa. Nearest qualified station: CEDAR RAPIDS #1, IA US (USC00131319), 0.4 miles. Median last 32°F April 28. Median first 32°F October 12. The 50% growing-season length is 166 days.

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32°F probabilities at this station

	10%	50%	90%
Last 32°F on or after	May 13	April 28	April 14
First 32°F on or before	September 29	October 12	October 25

Column order matches the NCEI file: for the last freeze, 10% is the later date and 90% is the earlier date. How to read the probabilities.

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Planting calendar

Frost dates for Iowa are above. Planting windows appear for states with a cited extension guide. The fall and seed tools use the numbers you enter and the station dates.

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