Deerfield climate

Deerfield Frost Dates and Growing Season

NOAA 1991-2020 normals for Chicago Botanic Garden, 5.9 km from Deerfield, elevation 630 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Chicago Botanic Garden. A median date has an even chance of a later freeze in spring, or an earlier one in fall.

The last spring freeze typically comes around April 26 and the first fall freeze around October 21, a growing season of about 176 days.

Median at 36°F
last May 8, first October 10
Median at 32°F
last April 26, first October 21
Median at 28°F
last April 13, first November 1

Last freeze in spring

The chance of a later freeze than the date shown. At 10 percent, one spring in ten still freezes after the date; planting after the 10 percent date for 32°F is the cautious choice.

Threshold10%20%30%40%50%60%70%80%90%
36°FMay 26May 21May 16May 11May 8May 5May 2Apr 29Apr 24
32°FMay 11May 6May 2Apr 30Apr 26Apr 23Apr 20Apr 16Apr 11
28°FApr 28Apr 23Apr 19Apr 16Apr 13Apr 10Apr 7Apr 4Mar 31
24°FApr 16Apr 10Apr 6Apr 3Mar 31Mar 29Mar 26Mar 21Mar 15
20°FApr 3Mar 31Mar 27Mar 24Mar 20Mar 17Mar 13Mar 9Mar 4
16°FMar 27Mar 21Mar 17Mar 14Mar 11Mar 8Mar 4Mar 1Feb 25

First freeze in fall

The chance of an earlier freeze than the date shown. At 10 percent, one fall in ten freezes before the date.

Threshold10%20%30%40%50%60%70%80%90%
36°FSep 28Oct 1Oct 4Oct 7Oct 10Oct 13Oct 16Oct 19Oct 24
32°FOct 5Oct 11Oct 14Oct 18Oct 21Oct 23Oct 26Oct 30Nov 2
28°FOct 17Oct 23Oct 26Oct 30Nov 1Nov 3Nov 6Nov 10Nov 14
24°FNov 1Nov 4Nov 7Nov 9Nov 12Nov 15Nov 19Nov 23Nov 28
20°FNov 8Nov 12Nov 15Nov 19Nov 22Nov 25Nov 28Dec 1Dec 7
16°FNov 15Nov 20Nov 24Nov 28Dec 1Dec 3Dec 7Dec 13Dec 20

Growing season length

Days between the last spring and first fall freeze at each threshold, with the chance of a season at least that long.

Threshold10%20%30%40%50%60%70%80%90%
36°F174166162158154150146141135
32°F197190185180176172167163155
28°F222216210206202198193187179
24°F247240234230225222217211205
20°F270262256252248243238234228
16°F289281275270266262257252244

How often it gets that cold

The share of years with at least one night at or below each temperature.

36°F or colder
100% of years
32°F or colder
100% of years
28°F or colder
100% of years
24°F or colder
100% of years
20°F or colder
100% of years
16°F or colder
100% of years

Degree days

A degree day is one degree of the daily mean temperature beyond a base, for one day. Heating degree days count cold (the fuel a house burns), cooling degree days heat, growing degree days the warmth a crop needs; each crop has its own base.

Heating degree days, base 65°F
6,366
Cooling degree days, base 65°F
806
Growing degree days, base 40°F
5,084
Growing degree days, base 45°F
3,952
Growing degree days, base 50°F
2,963
Growing degree days, base 55°F
2,110
Growing degree days, base 60°F
1,390

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January1,26200
February1,04902
March870222
April540680
May26444270
June64149536
July7269727
August8230687
September9796452
October39111159
November728027
December1,08803

What this means

NOAA computes these from the daily lows at the station over 1991-2020, fitting the dates of each year's last and first freeze to a distribution, so a date can be stated at any level of risk. 36°F is a frost risk for tender plants on a clear, calm night, since the ground cools below the air above it; 32°F is a freeze; 28°F is a hard freeze that kills most annuals.

The station is 5.9 km from Deerfield. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

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Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00111497 (Chicago Botanic Garden). Public domain.