Burdock Growing Information Arctium lappa Direct Seed: In spring after last frost date. Can be seeded in the fall in warmer regions. Spacing: 6-8” apart in rows that are 24-36” apart, at ½" depth. Growth needs: Grows best in deep, well-drained soil. Grows 1-2’ deep. Harvest: When at desired size, fall of 1st year or spring of 2nd year. Storage: 32° F at 95% humidity. Can be subject to wilt, so better stored and sold dirty.