Naperville, Illinois: planting zone & frost dates
Naperville is in USDA plant hardiness zone 5b, where the average coldest winter night reaches -15 to -10°F (-26.1 to -23.3°C). The typical last spring frost is around May 4 and the first fall frost around Oct 11.
Frost dates
| Probability | Last spring frost (32°F) | First fall frost (32°F) |
|---|---|---|
| Safer (10% risk) | May 14 | Oct 1 |
| Typical planning date (30% risk) | May 4 | Oct 11 |
| Median (50%) | Apr 28 | Oct 16 |
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 LISLE-MORTON ARBORETUM, IL (USC00115097), 6.3 mi (10.2 km) from the city center and 20 ft lower than the city center (-6 m). Record used for the 1991–2020 normals: 13 years.
Why your yard may differ from the station: microclimates.
Hardiness zone across Naperville
Naperville spans more than one half-zone. Share of the city's land area by zone (via its 4 ZIP codes): 5b (77%), 6a (23%). The headline zone is the one covering the most land. Look up your ZIP for your exact zone.
Vegetable planting calendar for Naperville
Dates are counted from the 30%-risk frost dates above (last frost May 4, first frost Oct 11). 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 9 – Mar 23 | May 11 – May 25 | — | — |
| Pepper | Feb 23 – Mar 9 | May 18 – Jun 1 | — | — |
| Lettuce | Mar 23 – Apr 6 | Apr 20 – May 11 | Apr 6 – May 18 | Aug 2 – Aug 30 |
| Green Beans | — | — | May 11 – Jun 15 | Jul 19 – Aug 2 |
| Sweet Corn | — | — | May 11 – Jun 8 | — |
| Zucchini & Summer Squash | Apr 6 – Apr 13 | May 11 – May 25 | May 11 – Jun 1 | Jul 19 – Aug 2 |
| Cucumber | Apr 6 – Apr 13 | May 18 – May 25 | May 11 – Jun 1 | Jul 19 – Aug 2 |
| Carrot | — | — | Apr 13 – May 18 | Jul 19 – Aug 2 |
| Onion | Feb 9 – Feb 23 | Apr 6 – Apr 20 | — | — |
| Potato | — | Apr 6 – Apr 27 | — | — |
| Basil | Mar 23 – Apr 6 | May 18 – Jun 1 | May 18 – Jun 8 | — |
| Spinach | — | — | Mar 23 – Apr 20 | Aug 16 – Sep 13 |
| Kale | Mar 9 – Mar 23 | Apr 6 – Apr 27 | Apr 6 – Apr 27 | Aug 2 – Aug 30 |
| Broccoli | Mar 9 – Mar 23 | Apr 20 – May 11 | — | Jul 19 – Aug 2 |
| Peas | — | — | Mar 23 – Apr 13 | Aug 2 – Aug 16 |
| Eggplant | Feb 23 – Mar 9 | May 18 – Jun 1 | — | — |
| Cabbage | Mar 9 – Mar 23 | Apr 6 – Apr 20 | — | Jul 19 – Aug 2 |
| Radish | — | — | Mar 30 – May 18 | Aug 30 – Sep 27 |
| Strawberry | — | Apr 6 – Apr 27 | — | — |
| Beets | — | — | Apr 13 – May 25 | Aug 2 – Aug 16 |
Nearby cities in Illinois
- Aurora — zone 5b, last frost Apr 25, first frost Oct 18
- Joliet — zone 6a, last frost Apr 26, first frost Oct 20
- Schaumburg — zone 5b, last frost May 6, first frost Oct 8
- Elgin — zone 5b, last frost May 1, first frost Oct 12
- Cicero — zone 6a, last frost Apr 17, first frost Oct 26
- Chicago — zone 6a, last frost Apr 17, first frost Nov 1
More: all Illinois cities · other zone 5b cities: Madison, WI, Des Moines, IA, Aurora, IL, Fort Collins, CO, Rockford, IL, Elgin, IL, Greeley, CO, Green Bay, WI
Naperville gardening questions
When is the last frost in Naperville, IL?
Plan around May 4. At NOAA's Lisle-morton Arboretum, IL station, 6.3 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 28, and after May 14 the risk drops to about 1 in 10. A hard freeze (28°F) usually ends earlier, around Apr 16. The 90% and 10% dates are 30 days apart, close to the 36-day median for cities on this site.
When should I plant tomatoes in Naperville, IL?
Start seeds indoors Mar 9 – Mar 23 and set transplants outside May 11 – May 25, once nights stay above 50°F and the soil is near 60°F. That leaves 160 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 Naperville?
About 169 days without a 32°F frost in a typical (median) year. In 9 years out of 10 the season lasts at least 148 days, and in 1 year in 10 it runs 188 days or more. In fall there is a 10% chance of frost by Oct 1 and a 30% chance by Oct 11. That ranks 13th longest of 14 Illinois cities on this site.
When should I plant a fall garden in Naperville?
Count back from the first fall frost (Oct 11): transplant broccoli Jul 19 – Aug 2; sow kale Aug 2 – Aug 30; sow lettuce Aug 2 – Aug 30; sow radishes Aug 30 – Sep 27. Hardy crops keep growing through light frosts; the median 28°F hard freeze here is Oct 26. How the math works: succession and fall planting.
Did Naperville's hardiness zone change on the 2023 map?
No. Going by the zone that covers most of the city's land, Naperville is zone 5b on both the 2012 and the 2023 USDA maps (PRISM/OSU ZIP listings). About 42% of U.S. ZIP codes kept their half-zone in 2023. Why the 2023 map is warmer.
Is all of Naperville in zone 5b?
No. Zone 5b covers about 77% of the city's land; the rest is in 6a (23%), measured across the city's 4 ZIP codes. Check your own ZIP code in the table above or with the ZIP lookup.