When to Plant Kale in Illinois
Published: April 24, 2026
Illinois gardeners in Zone 5b have a 28-week frost-free window for kale (April 7 to October 22). Cool-season crops like kale do well here because the short, cool summers match the plant's temperature preferences naturally. This guide gives exact dates for Illinois based on your local frost calendar.
Kale Planting Dates for Illinois
| Start seeds indoors | March 3–10 |
| Last frost (average) | April 7 |
| Transplant outdoors | March 10–20 |
| Direct sow outdoors | March 10–20 |
| Expect first harvest | May 4 – May 24 |
| Fall crop start | August 27–September 6 |
| Fall harvest | October 21 |
| First fall frost (average) | October 22 |
Dates above assume Zone 5b, the most common zone in Illinois. Gardeners in cooler Chicago (Zone 5b) plant 1–2 weeks later; warmer Peoria (Zone 6a) can plant 1–2 weeks earlier.
⚠ Plant kale 3–5 weeks before last frost for spring. Best planted in late summer (6–8 weeks before first fall frost) for fall/winter harvest. Frost sweetens the flavor.
Growing Kale in Illinois's Climate
Illinois's cold Zone 5b climate is close to ideal for kale. The cool springs and moderate summers match the plant's natural temperature preferences, producing crisp, sweet, slow-bolting harvests that hot-climate gardeners cannot grow.
The fall kale crop in Illinois is often better than the spring crop. Plants mature as temperatures cool in September and October, concentrating sugars and tightening heads or roots. Light frost can improve flavor; hard frost signals harvest time.
Common kale pests to watch for in Illinois include Cabbage Worm and Cabbage Looper. The first line of defense is companion planting: Onion and Garlic planted nearby discourage several of these pests by confusing host-plant identification or repelling adults before they can lay eggs. Weekly garden walks in the early morning catch problems when they're still manageable.
Kale Garden Calendar for Illinois
| Month | Task | Notes |
|---|---|---|
| January | — | Dormant season |
| February | — | Dormant season |
| March | Transplant outdoors | Soil temp must be 40°F+; nighttime lows above 50°F |
| April | Harden off seedlings | Set seedlings outdoors 1–2 hours daily, increasing gradually |
| May ← | Watch for bolting | Harvest promptly; spring heat arrives quickly |
| June | — | Dormant season |
| July | — | Dormant season |
| August | Fall crop planting | Transplant or direct sow for fall harvest before frost |
| September | — | Dormant season |
| October | First frost approaches | Harvest remaining kale; cover plants on frost nights |
| November | — | Dormant season |
| December | — | Dormant season |
Kale Growing Tips for Illinois Gardeners
- •Harvest outer leaves first using the cut-and-come-again method; the central growing point will produce for months.
- •Kale leaves become sweeter after the first frost as plants convert starches to sugars — wait for cold nights for best flavor.
- •Illinois's short growing season means start seeds indoors under grow lights — don't rely on windowsill light which produces leggy, weak seedlings that struggle outdoors.
- •Cover young transplants with floating row covers for the first 2–3 weeks outside. The 3–5°F of protection reduces frost damage risk and accelerates early growth.
- •Use floating row covers to block cabbage white butterflies from laying eggs on plants.
Companion Planting for Kale in Illinois
In Illinois's cold climate, planting kale with Onion and Garlic helps deter pests and improve soil. Avoid planting near Tomato and Strawberry, which inhibit kale growth through root chemistry or shared pest pressure. See the full kale companion planting guide for the complete list.
Kale Planting Dates by City in Illinois
Top cities in Illinois — select for city-level frost dates and planting calendars.
Frequently Asked Questions
When should I plant kale in Illinois?
In Illinois (Zone 5b), start kale seeds indoors around March 3–10 and transplant outdoors around March 10–20 — 4 weeks before the state's average last frost of April 7.
What is the last frost date in Illinois?
Illinois's average last frost date is April 7 in the state's most common Zone 5b. Frost dates vary by city — higher elevations and northern counties run 1 to 3 weeks later than the state average. See the city list below for city-level frost dates.
Can I grow kale year-round in Illinois?
kale is a cool-season crop in Illinois, with spring and fall windows. Summer heat bolts the plants before they can produce a harvestable crop. Succession planting every 2–3 weeks stretches the harvest window.
What kale varieties grow best in Illinois?
For Illinois's Zone 5b, consult a local nursery or extension office for kale variety recommendations.
When do I start kale seeds indoors in Illinois?
Start kale seeds indoors in Illinois around March 3–10, which is 5 weeks before the state's average last frost of April 7. Use grow lights and keep soil temperatures at 70–75°F for fastest germination.