Frost dates for Joliet, Illinois
In Joliet, half of springs have had their last frost by April 19 (and 1 spring in 10 still has one after May 7), and half of falls have had their first frost by October 25, leaving about 188 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
Joliet, Illinois
Last spring frost
April 19
Half of springs have their last frost by this date. For a safer bet, wait until May 7: only 1 spring in 10 has a frost after that.
First fall frost
October 25
Half of falls have their first frost by this date. In 1 fall in 10 it comes by October 12.
Growing season
188 days
Frost-free days in a typical year. 9 years in 10 get at least 167.
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: 3 in 5b and 5 in 6a.
Print a year planner for Joliet
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 3 | April 19 | May 7 |
| First frost in fall | October 12 | October 25 | November 6 |
The frost-free season between them runs 188 days in a typical year. In 1 year in 10 it is 208 days or longer, and in 1 year in 10 it is 167 days or shorter.
- Hard freeze (28°F): typically last on April 5 and first on November 4. 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 1 and first on October 15. 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 Joliet comes between April 3 and May 7, a window of 34 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, 41 percent have their typical last frost later than Joliet does.
Planting calendar for Joliet
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 1 to March 1 | Broccoli and cabbage Start seeds indoors | 5 to 7 weeks before planting them out |
| February 15 to March 15 | Cauliflower Start seeds indoors | 5 to 7 weeks before planting out |
| March | ||
| March 1 to 22 | Eggplant Start seeds indoors | 6 to 9 weeks before planting out |
| March 8 to 22 | Peppers Start seeds indoors | 6 to 8 weeks before planting out |
| March 15 to 29 | Tomatoes Start seeds indoors | 5 to 7 weeks before planting out |
| March 22 to April 5 | Peas, spinach, lettuce, radishes, onion sets, turnips Sow outdoors, as early as | hardy crops: 2 to 4 weeks before the typical last frost |
| March 22 to April 5 | Broccoli and cabbage Plant out, as early as | hardy crops: 2 to 4 weeks before the typical last frost |
| April | ||
| April 5 to 19 | Beets, carrots, potatoes, Swiss chard Plant outdoors, as early as | semi-hardy crops: up to 2 weeks before the typical last frost |
| April 5 to 19 | Cauliflower Plant out, as early as | semi-hardy: up to 2 weeks before the typical last frost |
| April 19 | Snap beans, sweet corn, cucumbers, summer squash Sow outdoors around | tender crops: around the typical last frost date |
| May | ||
| May 3 | Tomatoes, peppers, eggplant Plant out from | very tender: 2 weeks or more after the typical last frost |
| May 3 | Melons, winter squash, pumpkins, lima beans Sow outdoors from | very tender: 2 weeks or more after the typical last frost |
| May 30 to June 13 | Cabbage for fall Start seeds | set the plants out by July 18 |
| June | ||
| June 19 to July 3 | Broccoli for fall Start seeds | set the plants out by August 7 |
| July | ||
| July 29 | 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 |
| August | ||
| August 2 | Carrots for fall Last date to sow | 70 days to harvest, plus 2 weeks for slower fall growth |
| August 3 | 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 7 | Peas for fall Last date to sow | 65 days to harvest, plus 2 weeks for slower fall growth |
| August 8 | 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 12 | Leaf lettuce and beets for fall Last date to sow | 60 days to harvest, plus 2 weeks for slower fall growth |
| August 22 | Turnips and kohlrabi for fall Last date to sow | 50 days to harvest, plus 2 weeks for slower fall growth |
| September | ||
| September 1 | Spinach for fall Last date to sow | 40 days to harvest, plus 2 weeks for slower fall growth |
| September 11 | Radishes for fall Last date to sow | 30 days to harvest, plus 2 weeks for slower fall growth |
| October | ||
| October 12 | 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 11 to 18 | 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 18 days later. That plans around May 7, 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 Joliet Brandon Road Dam (station USC00114530), 2 miles from the center of Joliet. It sits at about the same elevation, 540 feet above sea level. NOAA rates this station's record as standard: at least 24 of the 30 years, with gaps filled from nearby stations.
The same station also gives the frost dates for Shorewood and Manhattan.
Our ZIP code lookup matches these 6 ZIP codes to the same station, so they get the same dates: 60404, 60421, 60431, 60433, 60436, 60442. Hardiness zones are worked out separately for each ZIP code.
Nearby places
- Naperville, Illinois: last frost around April 25, first frost around October 19 (15 miles away)
- Aurora, Illinois: last frost around April 28, first frost around October 13 (20 miles away)
- Chicago, Illinois: last frost around April 11, first frost around October 31 (35 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.