When to Plant Collard Greens in Iowa
Published: April 24, 2026
Iowa gardeners in Zone 5b have a 28-week frost-free window for collard green (April 7 to October 22). Cool-season crops like collard green do well here because the short, cool summers match the plant's temperature preferences naturally. This guide gives exact dates for Iowa based on your local frost calendar.
Collard Green Planting Dates for Iowa
| Start seeds indoors | March 3–10 |
| Last frost (average) | April 7 |
| Transplant outdoors | March 17–27 |
| Direct sow outdoors | March 17–27 |
| Expect first harvest | May 16 – May 31 |
| Fall crop start | August 13–23 |
| Fall harvest | October 12 |
| First fall frost (average) | October 22 |
⚠ Direct sow or transplant collard greens 3–4 weeks before last frost. Extremely cold hardy — withstands temps to 15°F. Can be grown as a perennial in Zones 8+. Fall planting produces the best-flavored greens.
Growing Collard Greens in Iowa's Climate
Iowa's cold Zone 5b climate is close to ideal for collard green. 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 collard green crop in Iowa 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 collard green pests to watch for in Iowa include Cabbage Worm and Aphid. 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.
Collard Green Garden Calendar for Iowa
| Month | Task | Notes |
|---|---|---|
| January | — | Dormant season |
| February | — | Dormant season |
| March | Transplant outdoors | Soil temp must be 45°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 collard green; cover plants on frost nights |
| November | — | Dormant season |
| December | — | Dormant season |
Collard Green Growing Tips for Iowa Gardeners
- •Harvest outer leaves continuously once plants reach 10 inches — the central growing point produces for months.
- •In Zones 8+ collard greens often overwinter and produce for 2–3 years as a perennial.
- •Iowa'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.
- •Frost improves flavor dramatically — southern tradition is to wait for the first frost before harvesting.
Companion Planting for Collard Greens in Iowa
In Iowa's cold climate, planting collard green with Onion and Garlic helps deter pests and improve soil. Avoid planting near Tomato and Strawberry, which inhibit collard green growth through root chemistry or shared pest pressure. See the full collard green companion planting guide for the complete list.
Collard Greens Planting Dates by City in Iowa
Top cities in Iowa — select for city-level frost dates and planting calendars.
Frequently Asked Questions
When should I plant collard green in Iowa?
In Iowa (Zone 5b), start collard green seeds indoors around March 3–10 and transplant outdoors around March 17–27 — 3 weeks before the state's average last frost of April 7.
What is the last frost date in Iowa?
Iowa'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 collard green year-round in Iowa?
collard green is a cool-season crop in Iowa, 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 collard green varieties grow best in Iowa?
For Iowa's Zone 5b, consult a local nursery or extension office for collard-greens variety recommendations.
When do I start collard green seeds indoors in Iowa?
Start collard green seeds indoors in Iowa 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.