Heirloom / Open Pollinated Broccoli lacks tolerance to extreme heat. Direct seed Broccoli in the spring or start indoors 4-6 wks before the last frost. Plant seeds ½” deep in full sun, 4-6″ apart, in rows 18-36″ apart, when outdoor temperatures have reached 50°F. Germination usually occurs in 5-17 days in soil 55-75°F. Heirloom Broccoli plants should be thinned to 12-24″. Harvest center head before flower buds open, then harvest side shoots frequently for continuous production.