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Frost dates for Lisle-Morton Arboretum, Illinois

Half of years have their last spring frost by April 28, but 1 year in 10 still frosts after May 14.

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 14
1 year in 5
May 9
3 years in 10
May 4
2 years in 5
April 30
Half of years (the median)
April 28

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 7
3 years in 10
October 11
2 years in 5
October 13
Half of years (the median)
October 16
Growing season
about 169 days
Hardiness zones nearby
5b, 6a
Summer days
a usual high of about 28 °C83 °F
Lettuce and spinach run to seed
June to September, in hot, long days (how we know)

Summer and rain

A growing garden needs about 25 mm1 in of water a week, rain and watering together. Here is what a normal month brings.

Month by month

January
high ~0 °C31 °F · low ~-10 °C15 °F · rain ~56 mm2.2 in
February
high ~2 °C35 °F · low ~-8 °C18 °F · rain ~50 mm2 in
March
high ~8 °C47 °F · low ~-3 °C26 °F · rain ~60 mm2.4 in
April
high ~15 °C59 °F · low ~2 °C36 °F · rain ~97 mm3.8 in
May
high ~21 °C71 °F · low ~9 °C47 °F · rain ~122 mm4.8 in
June
high ~27 °C81 °F · low ~14 °C58 °F · rain ~112 mm4.4 in
July
high ~29 °C84 °F · low ~17 °C62 °F · rain ~108 mm4.2 in
August
high ~28 °C83 °F · low ~16 °C60 °F · rain ~110 mm4.4 in
September
high ~24 °C76 °F · low ~11 °C52 °F · rain ~85 mm3.4 in
October
high ~17 °C63 °F · low ~5 °C40 °F · rain ~91 mm3.6 in
November
high ~9 °C48 °F · low ~-1 °C30 °F · rain ~70 mm2.8 in
December
high ~3 °C37 °F · low ~-6 °C21 °F · rain ~59 mm2.3 in

Where these numbers come from

NOAA NCEI 1991–2020 Climate Normals, the Lisle-Morton Arboretum station (listed by NOAA as Lisle-Morton Arboretum, USC00115097), at 41.81, -88.07. 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

60101, 60103, 60106, 60107, 60108, 60120, 60126, 60133, 60137, 60139, 60143, 60148, 60157, 60163, 60164, 60169, 60172, 60181, 60185, 60187, 60188, 60189, 60190, 60191, 60193, 60194, 60439, 60440, 60441, 60446, 60490, 60491, 60514, 60515, 60516, 60517, 60521, 60523, 60527, 60532, 60540, 60555, 60559, 60561, 60565.

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