Companion planting involves integrating flowering plants into a vegetable patch to create a functional, self-regulating ecosystem. This time-tested horticultural practice goes beyond aesthetics by introducing a natural system of checks and balances that supports crop health. Strategic placement of flowers utilizes biological interactions to manage pests, enhance pollination, and improve soil structure. This approach transforms a monoculture plot into a diverse, productive habitat.
Flowers That Repel Garden Pests
Certain flowers discourage harmful organisms by releasing specific chemical compounds. French Marigolds (Tagetes patula) are known for controlling microscopic root-knot nematodes. Their roots exude alpha-terthienyl, a compound toxic to these worms, which damage the roots of plants like tomatoes and peppers. This protective chemical action is most effective when marigolds are planted densely and allowed to grow for a full season.
Nasturtiums (Tropaeolum spp.) provide a dual-action form of pest control. Their foliage and stems are highly attractive to common garden pests, especially aphids, causing insects to colonize the flower instead of nearby vegetables like brassicas. This functions as a sacrificial “trap crop,” diverting the pests to a location where they can be easily monitored and managed. Nasturtiums also possess a pungent scent that helps repel squash bugs and cucumber beetles by confusing them as they search for host plants.
The strong, volatile aromas of allium flowers, such as ornamental chives or flowering garlic, create an olfactory barrier. The sulfur compounds released by these plants repel organisms like slugs and thrips. Planting alliums strategically throughout the garden helps mask the scent of vulnerable crops, making it difficult for insects to locate their preferred food source.
Flowers That Attract Pollinators and Beneficial Insects
Many garden flowers provide essential nectar and pollen resources for beneficial insects. These beneficials include general pollinators, such as bees and butterflies, and predatory insects that feed on pests. Establishing a stable food source ensures these helpful creatures remain in the garden to protect and pollinate vegetables. The open structure and prolonged bloom of certain flowers are important factors in their effectiveness.
Umbellifer flowers, such as flowering dill, fennel, or Queen Anne’s Lace, attract tiny predatory insects. Their umbrella-shaped heads have numerous shallow, accessible florets. This structure is ideal for small beneficial insects, including parasitic wasps and syrphid flies, which have short mouthparts and require easy access to nectar. The larvae of these beneficials are highly effective at controlling aphids and caterpillars.
Borage (Borago officinalis) provides a prolific and fast-replenishing nectar supply, making it highly attractive to honeybees and bumblebees. These pollinators are essential for crops like squash and tomatoes. Borage’s distinct blue, star-shaped flowers also attract predatory wasps and lacewings, helping to keep pest populations in check throughout the season.
Zinnias are a popular choice because their long blooming period provides a steady nectar supply and serves as a landing platform for butterflies. Single-petal, open-centered varieties are more accessible to a wider range of pollinators than dense, double-flowered types. By offering a continuous food source from mid-summer until the first frost, zinnias help maintain high numbers of beneficial predators when vegetable crops are fruiting.
Flowers for Improving Soil Structure and Nutrients
Certain flowers offer physical and chemical benefits directly to the soil, provided by deep root systems or nutrient cycling. These flowering plants prepare the soil for annual vegetable production.
Comfrey (Symphytum spp.) has a long, vigorous taproot system that can extend several feet deep. These deep roots break up compacted soil layers, improving aeration and water penetration for shallower-rooted vegetables. Comfrey is also a dynamic accumulator because its roots draw up essential minerals, such as potassium and calcium, from the subsoil.
The harvested leaves of comfrey can be used as a nutrient-rich mulch in a practice called “chop-and-drop.” As the leaves decompose on the soil surface, they release accumulated minerals into the topsoil, making them available to neighboring plants. This organic process naturally fertilizes the vegetable patch, reducing the need for external soil amendments.
Flowering legumes, such as lupines or clovers, contribute to soil fertility through a symbiotic relationship with Rhizobia bacteria. These bacteria reside in root nodules and convert atmospheric nitrogen into a plant-usable form. When the legume plant dies back or is cut down, the fixed nitrogen is released into the soil, acting as a natural, slow-release fertilizer for subsequent vegetable crops.
Practical Planting Strategies and Specific Flower Pairings
Successful companion planting relies on strategic placement to maximize benefits. Flowers that repel pests or act as trap crops should be placed in close proximity to vulnerable vegetables. For instance, French Marigolds should be interplanted within tomato rows, ideally spaced about 12 to 18 inches away from the vegetable stem, to ensure their root exudates protect against nematodes.
Nasturtiums function best as trap crops when planted along the perimeter of the bed or underneath taller plants like kale or broccoli. This placement draws aphids and caterpillars away from the main crop without causing resource competition. For attracting beneficial insects, flowers should be planted in clusters or blocks of several plants, rather than scattered individually. Grouping flowers ensures a concentrated nectar source that is easily recognizable and worth the trip for pollinators.
Gardeners must also consider the size and growth habit of flowers to avoid unintentional negative interactions. Taller flowering plants, such as zinnias or sunflowers, should be situated on the north side of the garden. This prevents them from casting excessive shade on sun-loving vegetables. Competition for water and nutrients can also occur, so avoid planting flowers that require vastly different growing conditions directly next to each other. Nasturtiums prefer poorer soil, while heavy-feeding crops like corn require rich soil, making slight separation advisable.