Joliet, Illinois: planting zone & frost dates
Joliet is in USDA plant hardiness zone 6a, where the average coldest winter night reaches -10 to -5°F (-23.3 to -20.6°C). The typical last spring frost is around Apr 26 and the first fall frost around Oct 20.
Frost dates
| Probability | Last spring frost (32°F) | First fall frost (32°F) |
|---|---|---|
| Safer (10% risk) | May 7 | Oct 12 |
| Typical planning date (30% risk) | Apr 26 | Oct 20 |
| Median (50%) | Apr 19 | Oct 25 |
How to read this: after the spring "10% risk" date, a 32°F frost happens in only about 1 year in 10. In fall, the "10% risk" date is the early end — a frost before it happens about 1 year in 10.
Frost data comes from NOAA station JOLIET BRANDON RD DAM, IL (USC00114530), 2.5 mi (4.0 km) from the city center and 72 ft lower than the city center (-22 m). Record used for the 1991–2020 normals: 30 years.
Why your yard may differ from the station: microclimates.
Hardiness zone across Joliet
Joliet spans more than one half-zone. Share of the city's land area by zone (via its 8 ZIP codes): 6a (63%), 5b (37%). The headline zone is the one covering the most land. Look up your ZIP for your exact zone.
Vegetable planting calendar for Joliet
Dates are counted from the 30%-risk frost dates above (last frost Apr 26, first frost Oct 20). Shift a week later in cold spots or low-lying ground.
| Crop | Start indoors | Transplant / plant out | Direct sow | Fall crop sow/plant |
|---|---|---|---|---|
| Tomato | Mar 1 – Mar 15 | May 3 – May 17 | — | — |
| Pepper | Feb 15 – Mar 1 | May 10 – May 24 | — | — |
| Lettuce | Mar 15 – Mar 29 | Apr 12 – May 3 | Mar 29 – May 10 | Aug 11 – Sep 8 |
| Green Beans | — | — | May 3 – Jun 7 | Jul 28 – Aug 11 |
| Sweet Corn | — | — | May 3 – May 31 | — |
| Zucchini & Summer Squash | Mar 29 – Apr 5 | May 3 – May 17 | May 3 – May 24 | Jul 28 – Aug 11 |
| Cucumber | Mar 29 – Apr 5 | May 10 – May 17 | May 3 – May 24 | Jul 28 – Aug 11 |
| Carrot | — | — | Apr 5 – May 10 | Jul 28 – Aug 11 |
| Onion | Feb 1 – Feb 15 | Mar 29 – Apr 12 | — | — |
| Potato | — | Mar 29 – Apr 19 | — | — |
| Basil | Mar 15 – Mar 29 | May 10 – May 24 | May 10 – May 31 | — |
| Spinach | — | — | Mar 15 – Apr 12 | Aug 25 – Sep 22 |
| Kale | Mar 1 – Mar 15 | Mar 29 – Apr 19 | Mar 29 – Apr 19 | Aug 11 – Sep 8 |
| Broccoli | Mar 1 – Mar 15 | Apr 12 – May 3 | — | Jul 28 – Aug 11 |
| Peas | — | — | Mar 15 – Apr 5 | Aug 11 – Aug 25 |
| Eggplant | Feb 15 – Mar 1 | May 10 – May 24 | — | — |
| Cabbage | Mar 1 – Mar 15 | Mar 29 – Apr 12 | — | Jul 28 – Aug 11 |
| Radish | — | — | Mar 22 – May 10 | Sep 8 – Oct 6 |
| Strawberry | — | Mar 29 – Apr 19 | — | — |
| Beets | — | — | Apr 5 – May 17 | Aug 11 – Aug 25 |
Nearby cities in Illinois
- Naperville — zone 5b, last frost May 4, first frost Oct 11
- Aurora — zone 5b, last frost Apr 25, first frost Oct 18
- Cicero — zone 6a, last frost Apr 17, first frost Oct 26
- Schaumburg — zone 5b, last frost May 6, first frost Oct 8
- Elgin — zone 5b, last frost May 1, first frost Oct 12
- Chicago — zone 6a, last frost Apr 17, first frost Nov 1
More: all Illinois cities · other zone 6a cities: Chicago, IL, Denver, CO, Milwaukee, WI, Colorado Springs, CO, Omaha, NE, Aurora, CO, Lincoln, NE, Fort Wayne, IN
Joliet gardening questions
When is the last frost in Joliet, IL?
Plan around Apr 26. At NOAA's Joliet Brandon Rd Dam, IL station, 2.5 mi from the city center, there is a 30% chance of a 32°F frost after that date. Half of springs have their last frost by Apr 19, and after May 7 the risk drops to about 1 in 10. A hard freeze (28°F) usually ends earlier, around Apr 5. The 90% and 10% dates are 34 days apart, close to the 36-day median for cities on this site.
When should I plant tomatoes in Joliet, IL?
Start seeds indoors Mar 1 – Mar 15 and set transplants outside May 3 – May 17, once nights stay above 50°F and the soil is near 60°F. That leaves 177 days between the 30% frost dates, enough for most varieties including 80–85-day slicers. More: tomato planting dates by zone.
How long is the growing season in Joliet?
About 188 days without a 32°F frost in a typical (median) year. In 9 years out of 10 the season lasts at least 167 days, and in 1 year in 10 it runs 208 days or more. In fall there is a 10% chance of frost by Oct 12 and a 30% chance by Oct 20. That ranks 5th longest of 14 Illinois cities on this site.
When should I plant a fall garden in Joliet?
Count back from the first fall frost (Oct 20): transplant broccoli Jul 28 – Aug 11; sow kale Aug 11 – Sep 8; sow lettuce Aug 11 – Sep 8; sow radishes Sep 8 – Oct 6. Hardy crops keep growing through light frosts; the median 28°F hard freeze here is Nov 4. How the math works: succession and fall planting.
Did Joliet's hardiness zone change on the 2023 map?
Yes. Most of Joliet was zone 5b on the 2012 map and is zone 6a on the 2023 map — half a zone warmer, like about 56% of U.S. ZIP codes. The shift comes from a newer 1991–2020 averaging period plus more weather stations and better mapping; it does not mean last frost comes earlier. Why the 2023 map is warmer.
Is all of Joliet in zone 6a?
No. Zone 6a covers about 63% of the city's land; the rest is in 5b (37%), measured across the city's 8 ZIP codes. Check your own ZIP code in the table above or with the ZIP lookup.