When to Plant Broccoli in Iowa
Published: April 21, 2026
Iowa gardeners in Zone 5b have a 28-week frost-free window for broccoli (April 7 to October 22). Cool-season crops like broccoli 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.
Broccoli Planting Dates for Iowa
| Start seeds indoors | February 24–March 3 |
| Last frost (average) | April 7 |
| Transplant outdoors | March 10–20 |
| Direct sow outdoors | March 10–20 |
| Expect first harvest | May 9 – May 29 |
| Fall crop start | August 13–23 |
| Fall harvest | October 12 |
| First fall frost (average) | October 22 |
Growing Broccoli in Iowa's Climate
Iowa's cold Zone 5b climate is close to ideal for broccoli. 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 broccoli 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 broccoli pests to watch for in Iowa 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.
Broccoli Garden Calendar for Iowa
| Month | Task | Notes |
|---|---|---|
| January | — | Dormant season |
| February | Start seeds indoors | Use grow lights; warm soil to 70–75°F for best germination |
| 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 broccoli; cover plants on frost nights |
| November | — | Dormant season |
| December | — | Dormant season |
Broccoli Growing Tips for Iowa Gardeners
- •For spring: start indoors 6 weeks before last frost and transplant outdoors 4 weeks before last frost.
- •For fall: start indoors in summer — count 10 weeks back from your first fall frost date.
- •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.
- •Harvest heads before any yellow flowers open — once flowers show, flavor declines quickly.
Companion Planting for Broccoli in Iowa
In Iowa's cold climate, planting broccoli with Onion and Garlic helps deter pests and improve soil. Avoid planting near Tomato and Pepper, which inhibit broccoli growth through root chemistry or shared pest pressure. See the full broccoli companion planting guide for the complete list.
Broccoli 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 broccoli in Iowa?
In Iowa (Zone 5b), start broccoli seeds indoors around February 24–March 3 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 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 broccoli year-round in Iowa?
broccoli 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 broccoli varieties grow best in Iowa?
For Iowa's Zone 5b, De Cicco and Waltham 29 tolerate cold and produce secondary side shoots after main head harvest.
When do I start broccoli seeds indoors in Iowa?
Start broccoli seeds indoors in Iowa around February 24–March 3, which is 6 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.