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Frost dates for Hillsboro, Illinois

Half of years have their last spring frost by April 13, but 1 year in 10 still frosts after April 28.

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
April 28
1 year in 5
April 23
3 years in 10
April 19
2 years in 5
April 17
Half of years (the median)
April 13

First fall freeze

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

1 year in 10
October 10
1 year in 5
October 15
3 years in 10
October 18
2 years in 5
October 21
Half of years (the median)
October 24
Growing season
about 192 days
Hardiness zones nearby
6a, 6b
Summer days
a usual high of about 31 °C87 °F
Lettuce and spinach run to seed
May 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 ~4 °C38 °F · low ~-6 °C21 °F · rain ~64 mm2.5 in
February
high ~7 °C44 °F · low ~-4 °C25 °F · rain ~66 mm2.6 in
March
high ~13 °C55 °F · low ~1 °C34 °F · rain ~78 mm3.1 in
April
high ~20 °C68 °F · low ~7 °C44 °F · rain ~128 mm5 in
May
high ~25 °C78 °F · low ~12 °C54 °F · rain ~128 mm5.1 in
June
high ~30 °C86 °F · low ~17 °C63 °F · rain ~97 mm3.8 in
July
high ~32 °C89 °F · low ~19 °C67 °F · rain ~95 mm3.7 in
August
high ~31 °C87 °F · low ~18 °C65 °F · rain ~80 mm3.1 in
September
high ~28 °C82 °F · low ~14 °C57 °F · rain ~84 mm3.3 in
October
high ~21 °C70 °F · low ~8 °C46 °F · rain ~87 mm3.4 in
November
high ~13 °C55 °F · low ~2 °C35 °F · rain ~96 mm3.8 in
December
high ~6 °C43 °F · low ~-3 °C26 °F · rain ~66 mm2.6 in

Where these numbers come from

NOAA NCEI 1991–2020 Climate Normals, the Hillsboro station (listed by NOAA as Hillsboro HCN, USC00114108), at 39.16, -89.49. 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

62011, 62015, 62017, 62019, 62032, 62049, 62051, 62056, 62058, 62069, 62074, 62075, 62076, 62077, 62080, 62083, 62086, 62088, 62089, 62091, 62094, 62262, 62471, 62538, 62546, 62553, 62555, 62556, 62557, 62560.

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