Frost dates for Naperville, Illinois
In Naperville, half of springs have had their last frost by April 25 (and 1 spring in 10 still has one after May 12), and half of falls have had their first frost by October 19, leaving about 174 frost-free days in a typical year. Here is how sure those dates are, what they mean for planting, and where they come from.
Frost dates for
Naperville, Illinois
Last spring frost
April 25
Half of springs have their last frost by this date. For a safer bet, wait until May 12: only 1 spring in 10 has a frost after that.
First fall frost
October 19
Half of falls have their first frost by this date. In 1 fall in 10 it comes by October 5.
Growing season
174 days
Frost-free days in a typical year. 9 years in 10 get at least 153.
Hardiness zone
5b
2023 USDA map: the coldest night of winter averages −15°F to −10°F. It was 5b on the 2012 map too. ZIP codes within about 6 miles of the city's center: 9 in 5b and 4 in 6a.
Print a year planner for Naperville
Frost risk through the year
How sure are these dates?
A frost date is a probability, not a promise. NOAA worked out, from 30 years of nightly lows, how often the last spring frost and the first fall frost fall on each date. The middle column is the typical year. The outer columns are the early and late years that come about once a decade.
| Early year 1 in 10 | Typical year 1 in 2 | Late year 1 in 10 | |
|---|---|---|---|
| Last frost in spring | April 11 | April 25 | May 12 |
| First frost in fall | October 5 | October 19 | October 30 |
The frost-free season between them runs 174 days in a typical year. In 1 year in 10 it is 194 days or longer, and in 1 year in 10 it is 153 days or shorter.
- Hard freeze (28°F): typically last on April 14 and first on October 29. It is a harder freeze than the 32°F frost line, cold enough to damage many garden plants; how hardy a crop is decides whether it comes through. (The National Weather Service's own hard-freeze threshold varies from office to office.)
- Frost possible (36°F at the station): typically last on May 6 and first on October 7. On clear, still nights the ground can be several degrees colder than the thermometer, so frost can form on plants when the official reading is in the mid-30s.
In 8 springs out of 10, the last frost in Naperville comes between April 11 and May 12, a window of 31 days. That is about average for NOAA's stations (the typical window is 31 days).
Among Illinois's 170 NOAA stations with a frost every year, 16 percent have their typical last frost later than Naperville does.
Planting calendar for Naperville
These dates count from the typical last and first frosts, using the planting rules published by Colorado State University Extension (spring), Virginia Cooperative Extension (fall crops) and University of Minnesota Extension (garlic, where winters are hard). Weather in any one year can run early or late, so check the forecast before you plant tender crops.
| When | What to do | Why then |
|---|---|---|
| February | ||
| February 7 to March 7 | Broccoli and cabbage Start seeds indoors | 5 to 7 weeks before planting them out |
| February 21 to March 21 | Cauliflower Start seeds indoors | 5 to 7 weeks before planting out |
| March | ||
| March 7 to 28 | Eggplant Start seeds indoors | 6 to 9 weeks before planting out |
| March 14 to 28 | Peppers Start seeds indoors | 6 to 8 weeks before planting out |
| March 21 to April 4 | Tomatoes Start seeds indoors | 5 to 7 weeks before planting out |
| March 28 to April 11 | Peas, spinach, lettuce, radishes, onion sets, turnips Sow outdoors, as early as | hardy crops: 2 to 4 weeks before the typical last frost |
| March 28 to April 11 | Broccoli and cabbage Plant out, as early as | hardy crops: 2 to 4 weeks before the typical last frost |
| April | ||
| April 11 to 25 | Beets, carrots, potatoes, Swiss chard Plant outdoors, as early as | semi-hardy crops: up to 2 weeks before the typical last frost |
| April 11 to 25 | Cauliflower Plant out, as early as | semi-hardy: up to 2 weeks before the typical last frost |
| April 25 | Snap beans, sweet corn, cucumbers, summer squash Sow outdoors around | tender crops: around the typical last frost date |
| May | ||
| May 9 | Tomatoes, peppers, eggplant Plant out from | very tender: 2 weeks or more after the typical last frost |
| May 9 | Melons, winter squash, pumpkins, lima beans Sow outdoors from | very tender: 2 weeks or more after the typical last frost |
| May 24 to June 7 | Cabbage for fall Start seeds | set the plants out by July 12 |
| June | ||
| June 13 to 27 | Broccoli for fall Start seeds | set the plants out by August 1 |
| July | ||
| July 23 | Snap beans for fall Last date to sow | 60 days to harvest, plus 2 weeks for slower fall growth, plus 2 weeks because frost kills it |
| July 27 | Carrots for fall Last date to sow | 70 days to harvest, plus 2 weeks for slower fall growth |
| July 28 | Cucumbers for fall Last date to sow | 55 days to harvest, plus 2 weeks for slower fall growth, plus 2 weeks because frost kills it |
| August | ||
| August 1 | Peas for fall Last date to sow | 65 days to harvest, plus 2 weeks for slower fall growth |
| August 2 | Summer squash for fall Last date to sow | 50 days to harvest, plus 2 weeks for slower fall growth, plus 2 weeks because frost kills it |
| August 6 | Leaf lettuce and beets for fall Last date to sow | 60 days to harvest, plus 2 weeks for slower fall growth |
| August 16 | Turnips and kohlrabi for fall Last date to sow | 50 days to harvest, plus 2 weeks for slower fall growth |
| August 26 | Spinach for fall Last date to sow | 40 days to harvest, plus 2 weeks for slower fall growth |
| September | ||
| September 5 | Radishes for fall Last date to sow | 30 days to harvest, plus 2 weeks for slower fall growth |
| October | ||
| October 5 | Tomatoes, peppers, squash, melons, cucumbers Watch the forecast from | in 1 fall in 10 the first frost comes by this date; pick tender crops before a frost |
| November | ||
| November 5 to 12 | Garlic Plant cloves | one or two weeks after the typical first hard freeze (28°F), our reading of the first killing frost |
Want more insurance? Shift every spring date 17 days later. That plans around May 12, the date after which only 1 spring in 10 has a frost.
For spring bulbs such as tulips and daffodils, plant once the soil has cooled to about 50 to 55°F and keep going until a couple of weeks before the ground freezes. Our guide to fall planting explains how to tell.
Where these numbers come from
These dates come from NOAA's weather station West Chicago Dupage Airport (station USW00094892), 10 miles from the center of Naperville. It sits at about the same elevation, 750 feet above sea level. NOAA rates this station's record as representative: at least 10 of the 30 years, with the gaps filled from nearby stations.
The same station also gives the frost dates for Elgin, Wheaton, Bartlett, Carol Stream, Hanover Park, St. Charles, Glendale Heights and Glen Ellyn.
Our ZIP code lookup matches these 9 ZIP codes to the same station, so they get the same dates: 60134, 60139, 60174, 60175, 60183, 60184, 60185, 60188, 60190. Hardiness zones are worked out separately for each ZIP code.
Nearby places
- Aurora, Illinois: last frost around April 28, first frost around October 13 (7 miles away)
- Joliet, Illinois: last frost around April 19, first frost around October 25 (15 miles away)
- Chicago, Illinois: last frost around April 11, first frost around October 31 (25 miles away)
See frost dates across Illinois, or look up your own ZIP code for the station nearest you. Want the background? Read what a last frost date really means.