Marigolds, Myths, and Mites
I don't know if anyone else has heard that marigolds are a natural way to repel insects from your tomato plants, but let me say that it is patently false.
As an experiment, I decided to plant some marigolds around my tomato plants to see if they would repel pests. Two weeks after planting, clover mites started showing up on my plants, and the common denominator was that they were on leaves that were touching.....you guessed it.....a marigold flower. I inspected the flowers, and at least one on each plant had a colony of mites and eggs under the petals near the base of the flower.
Now it may be that they repel some pests, but the only bugs on my plants before the flowers made it into the mix were fungus gnats. So I'd rather just have the fungus gnats than both.
Many of you probably know this already and can sit back and chuckle at my noob enthusiasm, but for those of you thinking about planting marigolds to repel pests; don't waste your time.