Nematicide marigolds offer a natural method to combat nematodes. Indeed, marigold roots secrete a substance that prevents the development of nematodes. In association with tomatoes (2 marigolds for 6 tomato plants) they protect them from the aggression of these pests. They can also be grown as a soil improver. In this case, it must be sown broadcast on the plot you wish to improve, and once the plant is sufficiently developed (be careful not to let it go to seed!), simply mow it and bury it in the soil with a spade or a cultivator. This contribution of fresh matter will enrich and fertilize the soil while bringing back to the surface some of the elements that the deep roots of the plant will have drawn from deep down (nitrogen, phosphate, etc.) and will favor the following crops.