Gardening Articles: Care :: Seeds & Propagation
by Charlie Nardozzi
If you thought broccoli was a once-a-year, one-shot affair, think again. Just about any gardener in the United States can harvest crops two, or even three times a year. How? In most areas, by sowing seed in July. For that third harvest of the year, gardeners in zones US Hardiness Zone 7b through 9a can sow certain varieties again in late summer for an overwintering crop. You'll find all the whys and wherefores later in the article, but you'll have to know first what zone you live in.
Standard broccoli planting strategy calls for sowing seed in spring. Specifically, sow seeds indoors 6 to 8 weeks before the last spring frost and transplant into the garden 3 to 4 weeks later for an early summer harvest. While this schedule is fine in most regions, only gardeners in northern, short-season zones 3 to 4a are limited to it. These gardeners, in cities such as Bismarck, Minneapolis, and Montpelier, Vermont, should choose any of the standard southern European varieties from the list below.
Gardeners in zones 9b and 10 are similarly limited, but to the opposite season. Cool spring is too short, and summer is too hot in zones 9b and 10 for broccoli. In cities such as Houston, New Orleans, Phoenix, and Orlando, sow seed in fall for an early spring harvest. Choose any variety from the list below.
If you live in zones 4b to 6a: Although the cold temperatures and shorter days of fall come quickly in the North, you can harvest an early summer crop from a late spring planting; or harvest in September and October from an early summer (June or July) planting. For the latter, choose a variety that matures quickly and that has good frost tolerance, such as 'Green Valiant', in case there's an early frost.
Start seeds indoors or direct sow into the garden 10 to 12 weeks before the first expected frost in your area. If you buy transplants, plant them 6 to 8 weeks before the first frost. For best germination when direct seeding, sow seeds about 3/4 to 1 inch deep, keep the soil moist and shaded. Whether you start with seeds or transplants, planting in midsummer means heat is likely to stress young broccoli plants. Provide afternoon shade until harvest by erecting shade cloth, or grow broccoli plants in north-south rows on the east side of tall summer crops, such as pole beans and sweet corn.
If you live in zones 6b to 7a: Summer comes quicker in these regions, so gardeners here are better off forgoing the spring crop and planting only for a fall crop following the planting schedule outlined in the previous section.
To stagger the fall harvest, plant broccoli blends (such as George's Favorite Blend, which mixes three or four varieties together) or make your own blend by planting some early, midseason, and late-maturing varieties simultaneously. This way you can stretch your harvest season from October to perhaps January.
If you live in zones 7b to 9a: Gardeners in these zones can grow any of the standard broccolis for a fall harvest (again following the directions above) as well as the northern European overwintering varieties of broccoli. Transplanted in late summer these varieties grow slowly through the winter and head up in March to May.
NG test gardeners planted these overwintering broccolis last fall and several reported good results to temperatures as low as 10° F. And Tim Peters at Peters Seed and Research Company tells me that one variety, 'Spring Green Mix', is hardy to 0° F.
Most of these genetically distinct strains of broccoli look like familiar market broccoli, which originated in southern Europe. Others look more like cauliflower and some have purplish shoots.
These overwintering types need a cold period to head properly. That's why, in contrast to the standard varieties, these succeed only as overwintered crops in zones 7b to 9a.
Start overwintering broccolis early in summer and transplant them in August, so plants have time to grow by January. Plants that are either too small or too large at the onset of low temperatures will suffer. Also, don't overfertilize. Use one-half the recommended rate -- about 3/4 cup of 5-10-10 per plant -- at planting time and apply the other half the following spring.