Many claims have been made about plants that repel mosquitoes and no-see-ums (gnats and midges). Plants that seem to be mentioned most often are feverfew, pennyroyal, citronella grass, lavender, catnip and marigold.
Biting insects look for blood from living things that emit carbon dioxide, and mosquitoes can sense it from far away. There are some plants that help mask that scent and in a sense hide the animal from these blood suckers.
Feverfew (Tanacetum parthenium): Feverfew is said to be effective in repelling mosquitoes and other flying biting insects and is ideal for planting around outdoor seating areas.
Pennyroyal (Mentha pulegium): Pennyroyal helps to repel mosquitoes and the infamous no-see-ums and is often used in commercial natural insect repellent creams and sprays.
Citronella grass (Cymbopogon nardus): Citronella is a well-known mosquito repelling plant. The oil from the plant is also added to candles that when lit help discourage mosquitoes from approaching.
Lavender (Lavandula angustifolia): In addition to repelling insects, lavender has a pleasant scent that is said to calm the nerves and promote relaxation.
Catnip (Nepeta cataria): Although cats love it, mosquitoes hate it.
Marigolds (Tagetes spp.): The smell of marigolds is so strong that it repels insects and might repel some people as well.