(Brassica oleracea gemmifera) Romans grew the ancient precursor to Brussels sprouts as far back as the 1200s. The plant as we know it today was developed in Belgium and the French introduced it into the U.S. in the 18th century. Brussels sprouts love cool weather and can tolerate frost, but they cannot handle excessive heat and struggle in temperatures above 75 degrees F. For regions with hot summers and mild winters, they perform well when grown over the winter. For those with harsh winters, try planting very early in spring and again in midsummer for a late harvest. Start seeds indoors several weeks before the last frost date and set plants out 24 inches apart after the chance of hard frost has passed, or direct sow ¼ inch to ½ inch deep in rich soil with full sun and abundant moisture. They are best when harvested after a light frost.