Frost dates for Decatur Airport, Illinois
Half of years have their last spring frost by April 16, but 1 year in 10 still frosts after April 30.
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 30
- 1 year in 5
- April 25
- 3 years in 10
- April 22
- 2 years in 5
- April 20
- Half of years (the median)
- April 16
First fall freeze
How often the first freeze comes on or before each date.
- 1 year in 10
- October 7
- 1 year in 5
- October 12
- 3 years in 10
- October 16
- 2 years in 5
- October 20
- Half of years (the median)
- October 22
- Growing season
- about 187 days
- Hardiness zone nearby
- 6a
- Summer days
- a usual high of about 29 °C84 °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 ~2 °C35 °F · low ~-7 °C20 °F · rain ~50 mm2 in
- February
- high ~4 °C40 °F · low ~-5 °C23 °F · rain ~47 mm1.8 in
- March
- high ~11 °C52 °F · low ~0 °C32 °F · rain ~64 mm2.5 in
- April
- high ~18 °C64 °F · low ~6 °C42 °F · rain ~93 mm3.7 in
- May
- high ~24 °C74 °F · low ~12 °C53 °F · rain ~111 mm4.4 in
- June
- high ~28 °C83 °F · low ~17 °C62 °F · rain ~111 mm4.4 in
- July
- high ~30 °C86 °F · low ~19 °C66 °F · rain ~84 mm3.3 in
- August
- high ~29 °C84 °F · low ~17 °C63 °F · rain ~77 mm3 in
- September
- high ~26 °C79 °F · low ~13 °C55 °F · rain ~76 mm3 in
- October
- high ~19 °C66 °F · low ~7 °C44 °F · rain ~81 mm3.2 in
- November
- high ~11 °C51 °F · low ~1 °C34 °F · rain ~75 mm3 in
- December
- high ~4 °C40 °F · low ~-4 °C25 °F · rain ~54 mm2.1 in
Where these numbers come from
NOAA NCEI 1991–2020 Climate Normals, the Decatur Airport station (listed by NOAA as Decatur Ap, USW00003887), at 39.83, -88.87. 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
61735, 61750, 61756, 61813, 61818, 61830, 61839, 61855, 61856, 61882, 61914, 61925…
+22 moreShow fewer
61929, 61936, 61937, 62501, 62510, 62513, 62514, 62521, 62522, 62523, 62526, 62532, 62535, 62537, 62544, 62547, 62549, 62550, 62551, 62554, 62567, 62573.
Nearby stations
The nearest stations and how their last-frost dates compare. Together they show how frost varies across your area.
- Springfield #2, IL, last frost by April 15
- Rantoul, IL, last frost by April 21
- Hillsboro, IL, last frost by April 13
- Congerville 2 NW, IL, last frost by April 21
- Carlinville, IL, last frost by April 14
- Danville, IL, last frost by April 21
Other stations in Illinois.
- Peoria Greater Peoria Airport, IL, last frost by April 16
- Hennepin Wtr Trmt Plt, IL, last frost by April 24
- Belleville SIU Rsch, IL, last frost by April 12
- Park Forest, IL, last frost by April 23
- Aledo, IL, last frost by April 22
- Aurora, IL, last frost by April 19
- Lisle-Morton Arboretum, IL, last frost by April 28
- Carbondale Southern Il Airport, IL, last frost by April 9
When do I plant? · Where the dates come from
More ways Milpa can help
When do I plant? · What grows well together? · Plan my garden · What can I plant now? · Something wrong in the garden? · Keep a garden diary · Heard a tip?