Repellant plants emit odors or chemicals that kill or repel pests, or attract beneficial insects that prey on garden predators. Some of these plants can be made into teas or foliar sprays that are effective as insect repellents or fungicides. Planting flowers that repel garden pests offers an extra bonus of brightening up the garden with beautifully colored blooms and foliages.
Borage, Opal Basil and Petunias
Borage, opal basil and petunias all deter tomato hornworms. Borage also is an attractant plant for beneficial insects, and it also repels cabbage worms. Petunias deter asparagus beetles, leaf hoppers, Mexican bean beetle, aphids and other predatory insects. (Tea made with petunia leaves is a potent insect repellent).
Chervil, Nasturtiums and Rue
Aphids are deterred by chervil, nasturtiums and rue. Chervil also may deter slugs. Nasturtiums repel whiteflies, cucumber beetles and other pests. Rue repels fish moths, flea beetles, onion maggots, slugs, snails and Japanese beetles.
The flowers of C. cineraruaefolium have been used for centuries as botanical pesticides, while white varieties repel Japanese beetle, and C. coccineum kills root nematodes. Costmary is a tall variety of chrysanthemum that repels moths.
Dill and Lemon Balm
Squash bugs are repelled by dill and lemon balm. Dill also deters aphids and spider mites to a certain degree. (Dill also attracts tomato horn worm and should not be planted as a companion to tomatoes). Lemon balm repels many other garden pests as well. (Crushed leaves, rubbed onto the skin, repel mosquitoes).
Four O'Clocks, Larkspur and White Geranium
Four O'Clock, larkspur and white geraniums all attract Japanese beetles, but feasts on any of these foliages are highly toxic meals. (Four O'Clocks and larkspur also are toxic to humans and animals.)
Garlic, Soybeans and Tansy
Japanese beetles are deterred by garlic, soybeans and tansy. Soybeans also repel chinch bugs, and tansy repels striped cucumber beetles, squash bugs, ants and mice. Garlic additionally repels aphids, coddling moths, root maggots, snails and carrot root fly. There is evidence that garlic may repel deer. Foliar sprays made with garlic deter aphids, whiteflies and fungus gnats. (The sulfur in garlic works as a natural fungicide.)
Geraniums and Thyme
Thyme and geraniums deter cabbage worms. Geraniums also repel Japanese beetles.
Hyssops, Mint, Peppermint, Rosemary, Oregano and Sage
Hyssop, mint, peppermint, rosemary, oregano and sage repel cabbage moths, and all but oregano and rosemary are effective against flea beetles. Mint and peppermint also deter aphids. Mint also is effective against ants, fleas and rodents. Rosemary is effective against bean beetles and carrot flies. Oregano deters cucumber beetles.
Flax, Horseradish and Coriander
Tannin and linseed oils in flax repel Colorado potato beetles. Horseradish and coriander are potato beetle deterrents as well. Horseradish also is effective against blister beetles, and the root can be used to make an insecticide spray and anti-fungal tea. Coriander also deters aphids and spider mites when planted as a companion crop. (Spider mites also can be eliminated with a foliar spray made from coriander.)
Scented Marigolds and Dahlias
Scented marigold roots excrete a substance that deters soil nematodes when turned into the soil. Also, whiteflies and beetles find the marigold scent distasteful. The most effective varieties are French and Mexican marigolds. (Marigolds should not be planted with beans or cabbage.) Dahlias also repel nematodes.