Plant seeds 1⁄4-1⁄2 inches deep. Transplant or thin small plants to 15-18 inches apart in rows 32-36 inches apart. Transplants can be started in April for May planting. Cabbage prefers full sun, but will tolerate part shade.Heads are ready when firm and when the interior is dense. Heads will split when over mature; rapid growth due to excess moisture and fertility will also cause splitting.