Slugs are not deterred by marigolds, in fact, it is the opposite and slugs are actually attracted to the plants. If you are looking for how to get rid of slugs, or planning slug control methods, then planting marigolds will not do the trick. Marigolds can be used as a trap plant to attract slugs away from other plants, but they will actively not deter slugs. There are many slug-repellent plants that can be used in backyards, with pungent aromatic herbs like rosemary and lavender good at being used as barriers to protect other plants from slugs.