Illinois planting calendar

When to plant broccoli in Illinois — sow, transplant & harvest dates

Illinois is mostly USDA zone 6a (range 5a-7a). Dates below are derived from broccoli's frost tolerance and Illinois's frost window — not generic national averages.

Broccoli planting timetable for Illinois

Stage	When in Illinois	Anchor
Start seeds indoors	mid-March (March 14)	6 weeks before the last frost (late April)
Transplant outside	mid-April (April 11)	14 days before the last frost (late April)
First harvest (estimate)	late June (June 30)	~80 days from transplant

Dates are state-wide averages for the dominant zone. Local microclimates — elevation, urban heat, coastal moderation — can shift the window by 1-2 weeks. Use the frost-date calculator for a date tuned to your town.

Why Illinois's climate shifts the broccoli dates

Illinois's last spring frost averages late April and first fall frost mid-October, which sets the whole planting clock. Illinois has a productive continental Midwest climate. The south of the state runs nearly two half-zones warmer than the Chicago area. Sow early — broccoli bolt once daytime temperatures hold above 24 °C, so the earlier they go in, the longer the harvest.

Start seeds indoors 6–8 weeks before last frost; transplant outdoors 2–4 weeks before last spring frost when soil reaches at least 7 °C (45 °F). Mature plants withstand temperatures as low as −6 °C (21 °F). Heads button (form premature small curds) when exposed to temperatures below 10 °C (50 °F) for extended periods as young seedlings, so harden off carefully. In zones 8–10, a second crop is practical as a fall planting, set out in late summer for harvest before hard freezes.

Frost-risk note

Don't plant before late April — a hard freeze can still set young plants back. In the northern counties near the Wisconsin line (zone 5a) the safe date runs a week or two later.

Regional variation within Illinois

the northern counties near the Wisconsin line (zone 5a) runs roughly 1-2 weeks behind the state average; the far south near Cairo and Carbondale (zone 7a) can plant 1-2 weeks earlier.

Chicago — USDA zone 6a
Springfield — USDA zone 6a
Peoria — USDA zone 5b
Rockford — USDA zone 5b
Carbondale — USDA zone 7a

What else to plant in Illinois around then

The same early window suits peas, lettuce, spinach, and onion sets.

Quick-grow guide

Sun: Full sun — 6+ hours direct.
Soil temperature for germination: 7–29 °C (45–85 °F).
Spacing: 18–24 inches (45–60 cm) between plants.
Days to harvest: ~80 days from planting out.

Frequently asked questions

When is the best time to plant broccoli in Illinois?

In Illinois (mostly USDA zone 6a), sow broccoli indoors around mid-March, transplant outdoors mid-April (before the last frost, late April), and harvest from late June. Broccoli are cold-hardy — they tolerate frost and actively prefer cool weather, so they go in well before the last spring frost and bolt in summer heat.

What USDA zone is Illinois?

Most of Illinois sits in USDA hardiness zone 6a, with the state spanning roughly 5a-7a from the northern counties near the Wisconsin line (zone 5a) to the far south near Cairo and Carbondale (zone 7a). The last spring frost averages late April and the first fall frost mid-October.

Can you grow broccoli in Illinois?

Yes. Illinois's dominant zone 6a supports broccoli — the key is timing. Broccoli are cold-hardy — they tolerate frost and actively prefer cool weather, so they go in well before the last spring frost and bolt in summer heat.

Does the planting date change across Illinois?

the northern counties near the Wisconsin line (zone 5a) runs roughly 1-2 weeks behind the state average; the far south near Cairo and Carbondale (zone 7a) can plant 1-2 weeks earlier.

What else can I plant in Illinois around the same time?

The same early window suits peas, lettuce, spinach, and onion sets.

Source and methodology

State zone spans from the USDA Plant Hardiness Zone Map (2023); frost-date averages from NOAA Climate Data Online. Hot-state two-season timing cross-checked against the UF/IFAS Florida Gardening Calendar and the University of Arizona Cooperative Extension planting calendar. Curated by the Growli editorial team.