|My broad beans took forever to produce, and when I pulled the old vines up this fall, the roots looked like big clumps of peanuts.|
|The nodules on the roots were likely root-knot nematodes, microscopic worms that enter plant roots and stems and interfere with the plant's uptake of water and nutrients. These nematodes thrive in sandy soils that seldom freeze in the winter, and they peak in late summer. You can reduce their numbers by interplanting with marigolds and members of the cabbage family, which tend to repel the worms. You may even need to solarize your soil by wetting it down and covering it with a loose sheet of clear plastic for a month. The heat trapped under the plastic cooks the nematodes in the top few inches of soil. After this process, don't disturb the soil before planting.
For long-term control of nematodes, the best approach is incorporating organicmatter in the soil because it contains fungi that kill the nematodes. Crab shells, shrimp hulls, and eggshells are especially helpful because they stimulate the proliferation of microorganisms that eat chitin, a substance contained in nematode eggs.