Cabbages are often prone to clubroot if they are repeatedly planted on the same area. This disease is caused by a fungus that lives in the soil and can survive for a particularly long time. Infected cabbages have clubroots that are swollen and knobbly. The plant fails to develop well, can be severely weakened and, in cases of very heavy infestation, can die. You must remove and destroy all affected plants. Do not plant any cabbages or other crucifers on the spot for the next four years. As a preventative measure, ensure that the soil has a regular supply of lime as a slightly elevated pH level inhibits the development of club root compared to the optimal pH value.