Answer: There is much anecdotal evidence on the pest-deterring properties of marigolds, but not alot of scientific studies. One common story is that that marigolds planted around vegetable gardens repel whiteflies, but further research indicates that marigold roots secrete a substance that is absorbed by nearby vegetables, which repels the insects. I'm not sure you'd get the same effect on your roses, and I haven't heard that marigolds do anything to inhibit Japanese beetles. But it certainly doesn't hurt to try, as they make a nice filler around the base of the rose bushes.
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