When to Plant Broccoli

The rule behind broccoli timing

Broccoli timing is about one stage of growth: the weeks when the head forms. Utah State University Extension says broccoli does best when temperatures stay under 75°F, and Iowa State reports that days of 86°F or more with nights of 77°F or more can stop heads from forming. So every planting date works backward from a cool heading period, either in late spring before summer arrives or in fall as the weather cools.

The opposite risk is a long cold spell on a large plant. Clemson Extension notes that 10 or more days in a row between 35 and 50°F, after a period of good growth, can make cole crops bolt, and the bigger the plant, the more likely it is. That is why the advice is to plant young transplants a few weeks before the last frost rather than large plants as early as possible.

Spring planting

The dates for your zone above show the spring window. Within it, extension services differ by a couple of weeks. Utah State sets transplants out 2 to 3 weeks before the average last frost; Maryland Extension goes about 4 weeks before. Seeds sown directly in the garden can go in at roughly the same time: Utah State says alongside transplants, and Wisconsin about 3 weeks before the last frost.

Soil temperature limits direct seeding more than air temperature does. UC Cooperative Extension gives 40°F as the minimum soil temperature for broccoli seed to germinate and 60 to 85°F as the optimum, so seed sown into cold spring soil comes up slowly. Transplants skip that delay and, as Utah State points out, give an earlier harvest.

To raise your own, count back from the transplant date. Utah State sows 6 to 7 weeks ahead, Clemson 6 to 8 weeks, Maryland uses 5- to 7-week-old plants, and Iowa State only 4 to 5 weeks. Aim for a stocky plant with 4 to 6 true leaves. Older, rootbound transplants are more likely to form small premature heads, so a late start is safer than an early one.

Fall planting

For fall, work back from the harvest you want. Utah State recommends early-maturing varieties planted 50 to 75 days before the expected harvest date, and that harvest can fall several weeks after the first fall frost, because broccoli tolerates light freezes. Wisconsin suggests direct-seeding fall crops 10 to 12 weeks before the first killing frost. Regional examples:

• Mid-Atlantic: Maryland direct-seeds in mid-July or transplants by the first week of August, and notes that fall plantings often yield better than spring ones.
• Central Iowa: transplants go out between late June and early August for harvest from mid-September to late October.
• South Carolina: Clemson’s fall transplanting window runs from mid-August in the Piedmont to the end of September on the coast, and Clemson considers fall the best broccoli season there.

Fall transplants take less time to raise, about 5 to 6 weeks according to Clemson. Maryland adds that fall broccoli takes longer to mature than spring broccoli, so don’t plant too late.

Warm-winter areas

Where frost is rare, broccoli is a cool-season crop planted from late summer through winter.

• Florida: UF/IFAS gives planting windows from fall into late winter in north and central Florida and a shorter window in south Florida. It warns that plantings made in August or September face more heat-loving insects and diseases.
• Lower Rio Grande Valley, Texas: Texas A&M AgriLife sows seed in flats from early September to early December and transplants after 3 to 4 weeks. Plants should go in no earlier than early October and do best set out from mid-October on.
• Phoenix and the low desert: the University of Arizona’s Maricopa County calendar lists broccoli from late summer into winter and allows 90 to 100 days from transplants, longer than in cooler regions.

West of the Cascades

In western Oregon and Washington, gardeners can also grow overwintering sprouting broccoli. Oregon State University’s PNW 548 lists transplanting from mid-July to early August for harvest from February to April. These plants need a large leafy frame before winter, because cold weather triggers the shoots that are harvested in spring.