Kohlrabi (Brassica oleracea). Here’s a cabbage-relative with a difference: the main crop is the stem, which has been selected over the centuries to grow as an oblate sphere, about the size of an apple. Well grown, this stem is juicy and crisp, and tastes similar to a cabbage heart. The leaves are edible too, especially when young. This crop tolerates heat better than most cabbage relatives, and can be grown straight through the summer in most areas of the country.