Joliet, IL 60431 planting calendar
- USDA zone
- 5b−15 to −10 °F
- Last frost
- Apr 19avg, 32°F
- First frost
- Oct 25avg, 32°F
- Growing season
- 188days
Joliet, Illinois is in USDA plant hardiness zone 5b. Its average last spring frost is around April 19 and the first fall frost around October 25, giving a growing season of about 188 days (NOAA 1991–2020 normals, 32°F, median). Start tender crops like tomatoes and peppers indoors weeks before the last frost and set them out afterward; sow hardy crops such as peas, spinach, and lettuce before it. The planner below turns those frost dates into a printable per-crop planting calendar.
Joliet planting calendar
Each crop's windows are counted from Joliet's average frost dates. hatched = start seeds indoors, solid green = plant out, teal = a fall sowing, and the terracotta dot marks the estimated first harvest. Ranges are extension-guide planning guidance, not guarantees.
- Start indoors
- Plant out
- Fall sowing
- First harvest
| Crop | Frost tolerance | Start indoors | Plant out | First harvest | Fall planting |
|---|---|---|---|---|---|
| Tomato | Tender | Feb 22 – Mar 8 | Apr 26 – May 3 | Jun 25 – Jul 15 | — |
| Pepper | Very tender | Feb 8 – Feb 22 | May 3 – May 10 | Jul 2 – Aug 1 | — |
| Cucumber | Tender | Mar 22 – Mar 29 | Apr 26 – May 3 | Jun 15 – Jul 5 | — |
| Summer squash / zucchini | Tender | — | Apr 26 – May 3 | Jun 10 – Jun 25 | — |
| Bush bean | Tender | — | Apr 26 – May 3 | Jun 15 – Jun 25 | Aug 26 – Sep 5 |
| Sweet corn | Tender | — | Apr 19 – May 3 | Jun 18 – Jul 18 | — |
| Basil | Very tender | Mar 8 – Mar 22 | Apr 26 – May 3 | May 26 – Jun 10 | — |
| Lettuce | Half-hardy | Mar 8 – Mar 22 | Mar 22 – Apr 5 | May 6 – May 21 | Aug 12 – Aug 27 |
| Pea | Hardy | — | Mar 8 – Mar 22 | May 2 – May 17 | Aug 2 – Aug 17 |
| Spinach | Hardy | — | Mar 8 – Mar 22 | Apr 17 – Apr 27 | Aug 22 – Sep 1 |
| Carrot | Half-hardy | — | Mar 29 – Apr 5 | May 28 – Jun 17 | Jul 23 – Aug 12 |
| Broccoli | Half-hardy | Feb 22 – Mar 8 | Mar 22 – Apr 5 | May 16 – Jun 5 | Jul 28 – Aug 17 |
Data: NOAA NCEI U.S. Climate Normals 1991–2020 (public domain) and USDA Plant Hardiness Zone Map 2023. Planting windows synthesized from U.S. Cooperative Extension guides.
Frost & freeze dates
From NOAA's 1991–2020 Climate Normals at station USC00114530. The median (p50) is the average date; the 90%-safe column is the date the freeze has passed in about 9 years out of 10 (p10 for spring, p90 for fall) — the conservative date to plant after or harvest before.
| Threshold | Last spring — avg | Last spring — 90%-safe | First fall — avg | First fall — 90%-safe | Season (days) |
|---|---|---|---|---|---|
| 36°F | May 1 | May 18 | Oct 15 | Oct 27 | 166 |
| 32°F (freeze) | Apr 19 | May 7 | Oct 25 | Nov 6 | 188 |
| 28°F | Apr 5 | Apr 21 | Nov 4 | Nov 21 | 211 |
| 24°F | Mar 27 | Apr 9 | Nov 15 | Dec 1 | 234 |
32°F is the standard "freeze" line that damages tender crops; lighter 36°F frost can nip the most cold-sensitive plants, while hardy crops shrug off light frost down toward 28°F. Use the threshold that matches what you are protecting.
Growing degree days
Growing degree days (GDD) accumulate warmth above a base temperature over the year — a better predictor of crop development than the calendar alone. Warm-season crops need a long, warm GDD total; a short, cool GDD total favors greens and brassicas.
| Model | °F·days | Used for |
|---|---|---|
| Base 50°F (warm-season) | 3,179 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 5,358 | cool-season crops (brassicas, greens) |
Hardiness zone 5b
Joliet sits in USDA plant hardiness zone 5b on the 2023 map — meaning its average annual extreme minimum winter temperature is about −15 to −10 °F. That number tells you which perennials, shrubs, and trees reliably survive an average winter here; it does not set your planting dates, which come from the frost calendar above.
Explore more places in zone 5b, or see all USDA hardiness zones.
Frequently asked questions
- What USDA hardiness zone is Joliet?
- Joliet, Illinois is in USDA plant hardiness zone 5b on the 2023 map (average annual extreme minimum temperature −15 to −10 °F) — from the USDA Plant Hardiness Zone Map 2023, matched to this location's ZIP. See the methodology page for sources.
- When is the last frost in Joliet?
- The average (median) last spring frost at 32°F is around April 19, from NOAA's 1991–2020 climate normals at the nearest reporting station. Roughly one year in ten the last frost is as late as May 7, so wait until then before setting out frost-tender plants if you want to be safe.
- When is the first fall frost in Joliet?
- The average first fall frost at 32°F is around October 25. That leaves a growing season of about 188 days between the average last spring and first fall frosts.
- When should I start tomatoes in Joliet?
- Start tomato seeds indoors about Feb 22 – Mar 8 and transplant them outside about Apr 26 – May 3, once the danger of frost has passed. Estimated first harvest is around Jun 25 – Jul 15.
- How long is the growing season in Joliet?
- About 188 days at the 32°F threshold (NOAA 1991–2020, median) — the span between the average last spring frost (~April 19) and the average first fall frost (~October 25). Cold-hardy crops extend usable time at both ends; frost-tender crops fit inside it.
Sources & method
Frost, freeze, growing-season, and growing-degree-day figures are NOAA NCEI U.S. Climate Normals 1991–2020 for station USC00114530 (Joliet Brandon Rd Dam, 7.3 km away). The hardiness zone is the USDA Plant Hardiness Zone Map 2023, matched to this location's ZIP. Planting windows are computed by counting from the average last and first frost using per-crop offsets synthesized from U.S. Cooperative Extension guides — the full method and citations are on the methodology page.