Marigolds are a warm-season annual broadleaf. 

 

Marigolds are well-known for their ability to produce compounds (such as α-terthienyl) that are allelopathic to certain species of plant-parasitic nematodes. In this context, a straight, weed-free stand is established.

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Marigolds are also used as a component in "insect haven" mixtures - attracting various pollinators and insect predators.