Marigold or amarillo contains a chemical that is toxic to some pests in the soil, like nematodes.
Thus, it is good plant marigold together with vegetable or in between farm crops. Nematodes
are very tiny parasites or worm in the soil, river, sea, rotting wood or plants. They also thrive in
other parts of the plant like the roots, and in animals and insects.
Most nematodes are not harmful but even helpful in the fertilizing the soil however, their
danger lies in that they feed on roots, stems or leaves of plants they suck the nutrient.
From: Farmnews March-April 1986.