Several plants boast ant-repelling reputations. Grow them near vulnerable plants or next to your home's foundations and doorways to discourage garden ants from becoming indoor pests. Harvested and dried, these plants scare off ants when sprinkled indoors or in the garden. Ant-repelling herbs make particularly useful companions in the garden by preventing ants from "herding" damaging insects such as white flies and aphids onto nearby plants.
Tansy (Tanacetum vulgare) carries a true "don't cross me" reputation. Several pests reportedly won't go past a tansy patch, including ants, flies and mice. The tall, flowering herb makes a cheerful presence in the garden, with plentiful bright yellow blossoms and fernlike foliage. Give it light shade or full sun. It tolerates all but waterlogged soils. Grow it where it won't shade other plants. As a hedge planted behind roses and bramble berries, tansy helps discourage aphid-farming ants.
The flowers retain their pungent scent and bright colors when dried. They make ideal wreaths that do double-duty as both decoration and pest repellent. In days gone by, people wrapped food in tansy to help preserve it and discourage ants--a practice worth reviving for picnics and barbecues.
An excellent choice for shady, moist garden spots, pennyroyal (Mentha pulegium) helps discourage ants, aphids and fleas. Like all mints, pennyroyal spreads quickly and isn't fussy about growing conditions. Adding plenty of fertilizer into new beds helps get it off to a good start.
Grow pennyroyal along a north-facing foundation to keep ants from crossing the threshold. Rose growers often plant them at the base of specimen shrubs or rose arbors. As low-growers, pennyroyals are perfectly positioned to protect the bases of taller plants, or to edge borders containing flowers and other ant-vulnerable plants. Creeping pennyroyal grows only 6 inches high, while common pennyroyal seldom reaches beyond 12 inches.
Indoors, fresh or dried pennyroyal is a traditional "strewing herb." Scatter leaves under dog beds, in cupboards and near baseboards to discourage ants, fleas and mice.
Don't overlook pennyroyal's minty cousins. Spearmint, peppermint and catnip also prove useful in scaring ants away, according to Cass County (North Dakota) Extension Service So many members of the mint family make useful ant-deterrents that it's almost impossible not to find one which meets the height, hardiness and soil specifications of your garden.
Sometimes known as garden rue, Ruta graveolens grows to 2 feet and features handsome blue-green foliage and delicate yellow-green blossoms. It tolerates light shade but flowers best in full sun. Plant rue as a low-growing border, or as a companion to other plants. One of the few "anti-ant" plants which make a suitable houseplant, rue grows nicely in a sunny indoor location.
Use rue at a garden's border to keep ants from entering, or near a home's vulnerable entry points. Alternatively, plant them near roses, raspberries and fruit trees to prevent ants from farming aphids and other predatory insects.
Gardeners should bear a few cautions in mind before planting rue. According to herbalist Lesley Bremness, rue can irritate the skin to those allergic to it. Use gloves and long sleeves if sores appear, or avoid it altogether. In addition, don't plant rue next to the plants for which it inhibits growth, including basil and cucumbers.