Planting flowers and vegetables together in a garden bed is a practice that has grown from medieval medicinal gardens to what is known in France as potager-style gardening. Although the specifics of the technique called companion-planting may be open to debate, planting together vegetable and border plants, especially flowers, can enrich your garden's colors, textures and fragrances, help in deterring pests and attract beneficial pollinators.
1. Apothecary Heritage
Before modern medicine, gardeners made fewer strict distinctions among vegetables, herbs and flowers. Fragrant low-growing sweet alyssum (Lobularia maritima), hardy throughout the United States, was once believed to cure hydrophobia. A botanical cousin, the carrot (Daucus carota), was cultivated for eating and as a tonic for liver-related complaints. 17th century apothecaries grew varieties of sea holly (Eryngium maritimum), hardy in USDA zones 5 through 8, to treat liver, stomach and neurological disorders. Yarrow (Achillea millefolium), hardy in USDA zones 3 through 9, colored cloth and soothed cold symptoms. These Old World medicinal gardens were grouped by their growing habits rather than classed by plant type.
2. Partial-Shade, Flower-Bed Vegetables
Planting your garden with flowers and vegetables that share the same growing habits maximizes the productivity of your beds. Use lettuces (Lactuca spp.) of all kinds as an edging to flower beds in partial shade. Leaves can be oval, petal-shaped or ruffly with colors ranging from green shades to dark wine-red. While kale (Brassica oleracea acephala) prefers full sun, its tolerance for cool to cold soil and its long growing season let you mingle it with flowers in partial shade. Kale leaves can be blue-gray-green, white-edged or red-tinged, and decorative varieties have ruffled heads with cream and purple accents. Complement the colors of kale and lettuce with pink and red impatiens (Impatiens), which can grow in the partial shade provided by these vegetables. Impatiens is grown as an annual except in USDA zones 10 and 11.
3. Full-Sun Planting Combinations
The majority of annual flowers and vegetables require full sun and rich, well-drained soil to reach maturity in a single season. For potager gardeners, these needs present many opportunities to comingle colors and textures of foliage, fruits and blooms. Annual dahlias (Dahlia spp.) share similar light, soil and water needs with tomatoes (Lycopersicon esculentum), and their vivid colors complement bright tomato colors. Plant bush beans with cornflowers (Centaurea cyanus), self-seeding perennials in USDA zones 3 through 8, or with blue-flowered borage (Borage officinalis), which also self-seeds. Do not, however, plant beans with onions (Allium cepa) or other members of the onion genus, such as chives (Allium schoenoprasum) and leeks (Allium porrum), because they stunt each others' growth.
4. Beneficial Partnerships
Two of the best reasons to plant flowers and vegetables together are to maximize pollination and minimize pest damage. Planting an abundance of nectar and pollen-heavy plants will draw the bees, wasps and other insects that pollinate vegetable and fruit flowers. Bee balm (Monarda didyma), hardy in USDA zones 4 through 9; anise hyssop (Agastache foeniculum), hardy in zones 4 through 11; and lavender (Lavandula spp.), hardy in zones 5 through 9, all draw pollinators in large numbers to neighboring vegetable plants. Planting chives (Allium tuburosum) with roses (Rosa spp.), both hardy in USDA zones 3 through 9, can deter a number of rose insect pests.