Kohlrabi is a hardy biennial grown as an annual. Kohlrabi has a swollen globe-shaped stem that makes it look like a turnip growing on a cabbage root. Stems can be white, purple, or green and is topped with a rosette of long-stemmed blue-green leaves. Kohlrabi is milder and sweeter than either cabbage or turnip. Kohlrabi prefers rich well-drained soil in full sun.