Plant breeders have had a heyday with marigolds. In 1915, David Burpee of Burpee Seed Company began investing heavily in marigold development. Other seed companies followed suit and during the 1920's the color variations and forms increased dramatically. Burpee was the first seed company to introduce a white marigold, a hybrid of T. erecta. Marigolds are perfectly at home in the kitchen garden, where many people plant them not only for the cheery flowers but also because their pungent foliage may help repel aphids and other pests.
Studies done in Europe show that French marigolds are effective against harmful soil nematodes.
It seems the marigold roots contain a substance that's damaging to the nematodes. If you're thinking about trying this in your own garden, keep in mind the marigolds must be planted in a solid block to fill the nematode-infested soil, and they must be grown for a full season to do the job. The large seed germinates easily, either directly sown in the garden after the soil has warmed, or earlier indoors. Watch out for damping off if you start marigolds inside. Flowers will appear about eight weeks after sowing.