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Frost dates for Hennepin Wtr Trmt Plt, Illinois

Half of years have their last spring frost by April 24, but 1 year in 10 still frosts after May 10.

A frost date is really a percentile from 30 years of records at a nearby weather station: in about half of years a frost still comes after the median date. Both numbers are below, so you can choose the risk yourself.

The odds

Last spring frost

How often a frost still comes on or after each date.

1 year in 10
May 10
1 year in 5
May 4
3 years in 10
May 1
2 years in 5
April 28
Half of years (the median)
April 24

First fall freeze

How often the first freeze comes on or before each date.

1 year in 10
October 1
1 year in 5
October 8
3 years in 10
October 11
2 years in 5
October 14
Half of years (the median)
October 17
Growing season
about 174 days
Hardiness zone nearby
5b
Summer days
a usual high of about 29 °C85 °F
Lettuce and spinach run to seed
June to September, in hot, long days (how we know)

Summer heat

Month by month

January
high ~0 °C33 °F · low ~-10 °C15 °F
February
high ~3 °C37 °F · low ~-8 °C18 °F
March
high ~10 °C50 °F · low ~-2 °C28 °F
April
high ~17 °C63 °F · low ~3 °C38 °F
May
high ~24 °C74 °F · low ~10 °C50 °F
June
high ~28 °C83 °F · low ~15 °C60 °F
July
high ~30 °C86 °F · low ~17 °C63 °F
August
high ~29 °C85 °F · low ~16 °C61 °F
September
high ~26 °C79 °F · low ~11 °C53 °F
October
high ~19 °C66 °F · low ~5 °C42 °F
November
high ~11 °C51 °F · low ~-1 °C31 °F
December
high ~3 °C38 °F · low ~-7 °C20 °F

Where these numbers come from

NOAA NCEI 1991–2020 Climate Normals, the Hennepin Wtr Trmt Plt station (listed by NOAA as Hennepin Wtr Trmt Plt, USC00114013), at 41.26, -89.34. These are that station’s own records, unshifted. The further your garden is from it, the less exactly they describe your ground. The planner finds the nearest station to your garden and lowers its confidence with distance, so no number is presented as if it were measured in your garden.

Cold air also pools in low ground on the clear, still nights when frost happens, so a hollow can freeze while a slope a few hundred feet away does not. No table can know that about your garden. A few seasons of your own logged frosts can.

ZIP codes nearest this station

61301, 61312, 61315, 61316, 61317, 61320, 61322, 61323, 61326, 61327, 61328, 61329, 61334, 61335, 61336, 61337, 61340, 61349, 61354, 61356, 61359, 61362, 61363, 61368, 61376, 61379, 61537, 61540, 61560, 61565.

What can I plant here, and when? ›

Nearby stations

The nearest stations and how their last-frost dates compare. Together they show how frost varies across your area.

Other stations in Illinois.

All locations · All plants · Folklore, checked