Companion planting for healthy roses makes good scientific sense and is grounded in ancient gardening practices. Roses are subject to infestation by insects such as aphids and mites and there are companion plants that repel these pests. Often companion planting is done for aesthetic reasons and a dual purpose is accomplished biochemically. There are several specific plants to use as companions in the rose garden.
Companion planting for mutual biological benefit is as old as gardening wisdom, but it has gained the support of modern science in recent years. Native American people planted corn, beans and squash together and called it the "Three Sisters." Beans hold nitrogen in the soil for corn to use, and corn acts as a trellis for bean growth. Squash leaves block sunlight and prevent weed growth.
Companion planting with roses can be purely aesthetic or can serve as an organic method of disease and insect control. In formal gardens, low hedges are put around rose beds to hide the less attractive lower part of the plant. Many gardeners design their rose plantings with companion plants to hide the lower branches. Dianthus, catmint and lavender are good choices for this method. Parsley is attractive near roses and is also an insect repellent.
The modern cottage garden style uses roses as companion plants. A cottage garden is a densely planted, informal design that mixes ornamental plants with herbs and vegetables. Climbing roses traditionally adorn a cottage garden and are frequently paired with chives, garlic and pungent herbs like fennel and chervil. These herbs are good companions for roses because they repel aphids. Aphids attack new rose growth in the early spring.
Nasturtiums are a "trap crop" to companion plant with roses because aphids are attracted to their yellow flowers. Geraniums are also a trap crop that lures aphids and other insect pests away from roses. French marigolds are a traditional favorite for companion planting because they produce a pesticidal chemical from their roots so strong it lasts years after they're gone.
Weeds are a problem in every style of rose garden and there are companion plants that help. Some plants, such as marigolds, manufacture and release biochemicals that play a part in plant antagonism. They release a biochemical that prevents germination of some weeds. Marigolds are effective against weeds such as ground ivy, couch grass, bindweed and horsetail.