When is the last frost in Dekalb, IL?

The average last spring frost (50% probability of 32°F) in Dekalb is around April 24, based on NOAA/NCEI 1991–2020 normals at the De Kalb, IL station (2.4 mi away). Half of years it falls outside that date, so wait 1–2 weeks past it before setting out frost-tender plants.

When is the first fall frost in Dekalb?

The average first fall frost in Dekalb, IL is around October 18, giving roughly a 177-day frost-free growing season.

What planting zone is Dekalb, IL?

Dekalb is in USDA plant hardiness zone 5b (average annual extreme minimum temperature -15 to -10°F), from the 2023 USDA Plant Hardiness Zone Map.

What is the weather like in Dekalb?

In Dekalb, IL the warmest month is July (avg high 83.1°F) and the coldest is January (avg low 13.1°F). It averages about 37.3″ of precipitation a year and 33.1″ of snow.

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Dekalb, IL Planting Calendar & Frost Dates

USDA hardiness zone 5b · ZIP 60115 · elevation 266′ · NOAA & USDA data

Dekalb is in USDA hardiness zone 5b (winters can dip to -15 to -10°F), with a growing season of about 177 days between the average last spring frost (April 24) and first fall frost (October 18). The warmest month is July (avg high 83.1°F); the coldest is January (avg low 13.1°F). It averages 37.3″ of precipitation a year and 33.1″ of snow, mostly mid-winter. Start cool-season crops several weeks before the last frost; wait until after it for tomatoes, peppers and other tender crops.

Hardiness zone

min temp -15 to -10°F

Last spring frost

April 24

avg (50% prob, 32°F)

First fall frost

October 18

avg (50% prob, 32°F)

Growing season

177 days

frost-free window

Warmest month

July

avg high 83.1°F

Month-by-month typical weather in Dekalb

Average conditions from the NOAA/NCEI 1991–2020 U.S. Climate Normals at De Kalb, IL (2.4 mi away). Temperatures °F, precipitation & snow in inches.

Month	Avg high	Avg low	Mean	Precip (in)	Snow (in)
January	28.1	13.1	20.6	1.7	10.2
February	32.5	16.6	24.5	1.7	8.7
March	45	26.8	35.9	2.2	4.4
April	58.6	37.3	48	3.6	1.3
May	70.2	49.2	59.7	4.8	0
June	79.9	59.5	69.7	4.6	0
July	83.1	63.3	73.2	4	0
August	81.2	61.3	71.3	4.1	0
September	74.9	53.2	64	3.3	0
October	62	41	51.5	3	0.1
November	46.3	29.6	37.9	2.3	1.8
December	33.6	19.1	26.3	2	6.6

What to plant when in Dekalb

Crop	Season	What to do & when
Tomatoes	warm	Start seeds indoors: March 13 · Transplant out: May 1
Peppers	warm	Start seeds indoors: February 27 · Transplant out: May 8
Cucumbers	warm	Direct sow: May 1
Zucchini / squash	warm	Direct sow: May 1
Bush beans	warm	Direct sow: May 1
Sweet corn	warm	Direct sow: May 1
Basil	warm	Transplant out: May 1
Peas	cool	Sow (spring): March 20 · Sow (fall): August 23
Spinach	cool	Sow (spring): March 13 · Sow (fall): August 23
Lettuce	cool	Sow (spring): March 27 · Sow (fall): August 23
Kale	cool	Transplant (spring): April 3 · Sow (fall): August 9
Broccoli	cool	Transplant (spring): April 10
Carrots	cool	Sow (spring): April 3 · Sow (fall): August 9
Onions	cool	Transplant (spring): March 27
Potatoes	cool	Plant seed potatoes: April 10
Radishes	cool	Sow (spring): March 27 · Sow (fall): September 6

Dates are computed from Dekalb's average frost dates using standard cool-/warm-season timing. They're a starting point — a cold spring, a warm microclimate, or a fast-maturing variety can shift them by a week or two.

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Gear that helps you plant on time

Some links below are Amazon affiliate links (tag theboringthin-20). If you buy through them we may earn a small commission at no extra cost to you — it keeps this almanac free. We only list generic, genuinely-useful categories.

Soil thermometer →Know when the ground is warm enough to sow — the honest signal, not the calendar.Seed-starting trays + dome →Start tomatoes & peppers indoors on the schedule below.Seedling heat mat →Warms the soil for faster, more even germination indoors.Floating row cover / frost cloth →Buys you 4–8°F to beat an early or late frost.Raised garden bed kit →Warms and drains faster in spring than in-ground soil.Garden gloves →Basic kit for transplant day.

Nearby cities in Illinois

Carpentersville, IL Elgin, IL Aurora, IL Bartlett, IL Hoffman Estates, IL Streamwood, IL Hanover Park, IL Carol Stream, IL

Sources & method. Hardiness zone: 2023 USDA Plant Hardiness Zone Map (PRISM Climate Group, Oregon State University). Frost dates & growing season: NOAA/NCEI 1991–2020 U.S. Climate Normals, nearest station with published freeze normals — De Kalb, IL, 2.4 mi (confidence: high). Monthly weather normals: De Kalb, IL, 2.4 mi (confidence: high). ZIP centroid from U.S. Census 2023 ZCTA data. Frost dates are the 50%-probability date — half of years frost occurs outside the stated date. Nothing here is invented; where the nearest station is far, we say so. Last updated 2026-07-22.