Iowa · zones 4b–6a
When to plant broccoli in Iowa.
Sow or transplant between Mar 10 to Apr 7 in a typical year, keyed to Iowa's median last frost around May 1. A second, fall sowing fits Jun 23 to Aug 2. Dates below are state medians; your ZIP code shifts them by days to weeks.
The 2026 windows
Broccoli dates for a typical Iowa season.
1 · Start indoors
Jan 27 to Feb 24
About 6 weeks before set-out. Warm spot, real light.
2 · Set out
Mar 10 to Apr 7
Keyed to the ~May 1 last frost. Sow 0.5" deep, 18" apart.
Fall round
Jun 23 to Aug 2
Counted back from the ~Oct 7 first frost.
Harvest
~60 days later
~1.2 lb per plant over ~3 weeks.
Iowa spans more than one climate: Zone 5 is the most common zone, but the state runs 4b to 6a. That's why the planner works from your ZIP code's frost dates, not your zone: mountain and coastal gardens in the same state can be three weeks apart.
Iowa growing notes
Iowa's prairie soil feeds broccoli. Iowa's short season sets the schedule.
159 days means every week of head start counts
Iowa's frost-free window averages about 159 days statewide, running from an early-May last frost to an early-October first frost, though a garden in the state's far north can run 2 to 3 weeks shorter than one down near the Missouri line. Either way, broccoli's 70 days from seed eats a real chunk of that window if you wait to direct sow. Start transplants indoors 6 weeks before the last frost and set them out as soon as the soil can be worked, rather than waiting for guaranteed warmth; broccoli tolerates a light frost far better than the cold snaps that would set back a pepper or tomato.
Space transplants 18 inches apart, since a plant that keeps sending up side shoots for a month or more once the main head is cut needs the elbow room to keep producing. A fall planting, set out in midsummer for an autumn harvest, often outperforms the spring crop in Iowa: the plant finishes as days cool rather than heats up, and broccoli sweetens rather than turns bitter when it matures into falling temperatures.
The soil is doing more work than you think
Iowa sits on some of the deepest, richest prairie soil in the country, built up over thousands of years of tallgrass root systems, and that native organic matter, often 3 to 6 percent by weight where the ground has never been stripped, means broccoli here starts with more built-in fertility than gardeners in most other states get without years of compost. That head start does not eliminate the need for nitrogen, though; broccoli is one of the hungriest vegetables in the garden and still wants a side-dress of compost or blood meal about 3 weeks after transplanting, when the plant shifts from establishing roots to building the head.
Keep watering steady rather than letting the bed dry out between soakings, aiming for the equivalent of 1 to 1.5 inches a week; broccoli that goes through a dry stretch right as the head forms tends to bolt into loose, ricey florets instead of a tight dome, and that damage does not reverse once it starts.
Flea beetles hit early, cabbage worms hit all season
Flea beetles are the first threat, riddling young transplants with small shot-holes within days of setting them into cool Iowa spring soil; row cover laid immediately after transplanting, left on until the plants are established and vigorous, blocks them without any spray. Aphids follow later, clustering on the underside of leaves and in the developing head itself, where a strong jet of water from the hose knocked them loose every few days usually keeps the population from building into a real problem.
Cabbage worms and loopers are the season-long pest, green caterpillars that blend into the leaf color well enough to hide from a casual glance; check the undersides of leaves weekly for the pale yellow egg clusters and for the caterpillars themselves, and a Bt spray applied at the first sign of chewing damage controls them without harming the beneficial insects also active in an Iowa garden.
In Iowa: watch for
The pests that find broccoli here.
A middle-length season, about 159 frost-free days, means broccoli overlaps cabbage worms & loopers for a stretch each summer. Check plants every week or two and treat early.
Green caterpillars chewing ragged holes; green droppings.
Organic fix: Handpick, cover with netting, spray Bt.
Gray-green clusters tucked into the leaf folds.
Organic fix: Blast with water, then insecticidal soap.
Tiny holes peppering the young leaves.
Organic fix: Row cover from day one; diatomaceous earth.
Black rot
Yellow V-shaped wedges cutting in from the leaf edge, veins blackening inside.
Organic fix: Pull infected plants, water at the base, keep brassicas out of that bed 3 years.
Seedlings wilt, yellow and stall for no reason; white maggots tunnel the roots.
Organic fix: Row cover before the flies are up, when yellow rocket blooms; rotate the bed.
Your season math: Iowa gives broccoli about 159 frost-free days, and it needs roughly 60 days to a first harvest. It's a one-planting crop, so time that single sowing well.
Planting broccoli in Iowa: questions
When should I plant broccoli in Iowa?+
In a typical Iowa year, sow broccoli or set out transplants between Mar 10 to Apr 7, keyed to the state's median last frost around May 1. There's also a fall window: Jun 23 to Aug 2. Your exact dates shift with your ZIP code and microclimate.
When do I start broccoli seeds indoors in Iowa?+
Start seeds inside about 6 weeks before set-out: roughly Jan 27 to Feb 24 for a typical Iowa season.
What USDA zone is Iowa?+
Iowa spans zones 4b–6a, mostly zone 5. But frost dates, not zones, set planting time. The free planner uses your ZIP code's actual frost dates.
How many broccoli plants do I need?+
Depends who you're feeding. The crop page has exact counts per household size, or the free planner does the math for your family in about 60 seconds.