Frost dates for Harrisburg, Illinois
Half of years have their last spring frost by April 7, but 1 year in 10 still frosts after April 25.
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 25
- 1 year in 5
- April 18
- 3 years in 10
- April 14
- 2 years in 5
- April 10
- Half of years (the median)
- April 7
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 16
- 3 years in 10
- October 21
- 2 years in 5
- October 23
- Half of years (the median)
- October 26
- Growing season
- about 202 days
- Hardiness zones nearby
- 6b, 7a
- Summer days
- a usual high of about 31 °C88 °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 ~6 °C43 °F · low ~-4 °C24 °F · rain ~96 mm3.8 in
- February
- high ~9 °C48 °F · low ~-2 °C28 °F · rain ~80 mm3.1 in
- March
- high ~14 °C58 °F · low ~2 °C36 °F · rain ~124 mm4.9 in
- April
- high ~21 °C69 °F · low ~8 °C46 °F · rain ~134 mm5.3 in
- May
- high ~26 °C78 °F · low ~14 °C56 °F · rain ~110 mm4.3 in
- June
- high ~30 °C86 °F · low ~18 °C65 °F · rain ~125 mm4.9 in
- July
- high ~32 °C89 °F · low ~20 °C68 °F · rain ~89 mm3.5 in
- August
- high ~31 °C88 °F · low ~19 °C66 °F · rain ~91 mm3.6 in
- September
- high ~28 °C82 °F · low ~14 °C57 °F · rain ~79 mm3.1 in
- October
- high ~22 °C71 °F · low ~7 °C45 °F · rain ~96 mm3.8 in
- November
- high ~14 °C57 °F · low ~2 °C36 °F · rain ~101 mm4 in
- December
- high ~8 °C47 °F · low ~-2 °C29 °F · rain ~86 mm3.4 in
Where these numbers come from
NOAA NCEI 1991–2020 Climate Normals, the Harrisburg station (listed by NOAA as Harrisburg HCN, USC00113879), at 37.74, -88.52. 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
62817, 62829, 62856, 62859, 62867, 62869, 62871, 62890, 62917, 62930, 62934, 62935…
+8 moreShow fewer
62946, 62954, 62965, 62974, 62977, 62979, 62984, 62987.
Nearby stations
The nearest stations and how their last-frost dates compare. Together they show how frost varies across your area.
- Carbondale Southern Il Airport, IL, last frost by April 9
- Grand Chain Dam, IL, last frost by April 3
- Belleville SIU Rsch, IL, last frost by April 12
- Rochester Ferry, KY, last frost by April 15
Other stations in Illinois.
- Hillsboro, IL, last frost by April 13
- Carlinville, IL, last frost by April 14
- Decatur Airport, IL, last frost by April 16
- Springfield #2, IL, last frost by April 15
- Danville, IL, last frost by April 21
- Rantoul, IL, last frost by April 21
- Congerville 2 NW, IL, last frost by April 21
- Peoria Greater Peoria Airport, IL, last frost by April 16
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?