Companion planting is the practice of growing specific plants near each other for mutual benefit. When focused on tomatoes, this strategy involves selecting flowers to enhance plant health and increase yields. Flowers contribute by actively deterring harmful organisms or by supporting beneficial insects. Using the right floral companions can significantly reduce the need for chemical intervention.
Flowers That Deter Common Tomato Pests
Some flowers act as natural bodyguards for tomato plants by releasing compounds that repel or confuse common garden pests. This deterrence is achieved through strong scents that mask the tomato plant’s aroma or through root exudates toxic to soil-dwelling threats.
The French Marigold (Tagetes patula) is perhaps the most recognized flower for its pest-repelling qualities, primarily targeting root-knot nematodes. These flowers release a chemical compound called alpha-terthienyl from their roots, which is nematicidal and kills nematodes attempting to feed on the roots. For maximum effect, French marigolds should be planted closely, ideally 10 to 18 inches from the tomato base, or used as a dense cover crop before the season begins.
Nasturtiums (Tropaeolum majus) function as a trap crop for pests like aphids and whiteflies. These insects are highly attracted to the nasturtium’s sweet sap and congregate there, leaving the tomato plants untouched. The spicy scent may also confuse pests, preventing them from locating the tomato host plant. This strategic attraction allows the gardener to manage the pest population on the sacrificial flower.
Flowers That Support Beneficial Insects
A second strategy is planting flowers that attract insects which prey on or parasitize tomato pests. These beneficial insects include ladybugs, lacewings, and minute parasitic wasps, providing continuous pest control. Providing a consistent source of nectar and pollen is essential for keeping these organisms in the garden.
Borage (Borago officinalis) is known for its blue, star-shaped blooms. Its primary benefit is attracting parasitic wasps, which lay eggs inside the larvae of pests like the tomato hornworm. Borage also attracts bees, which can improve tomato flower pollination and fruit set, even though tomatoes are self-pollinating.
Sweet Alyssum (Lobularia maritima) is a low-growing flower that provides tiny, accessible nectar and pollen sources for small beneficial insects. These flowers are particularly attractive to hoverflies and minute parasitic wasps, which are highly effective predators of aphids and other soft-bodied pests. Planting Sweet Alyssum as a groundcover beneath the tomato plants helps maintain a steady population. Dill, another beneficial flower, attracts ladybugs and hoverflies, whose larvae consume aphids and spider mites.
Maximizing Effectiveness Through Placement
Integrating companion flowers requires ensuring they assist the tomatoes without competing with them. Since tomatoes are heavy feeders requiring full sun and consistent watering, floral partners should share similar requirements but not compete for resources. The goal is to establish a mutually beneficial relationship, not a competition.
Marigolds, acting as a repellent, should be placed within 12 to 24 inches of the tomato plants, allowing their root exudates to protect the soil. Nasturtiums, which are trap crops, require strategic placement slightly away from the main tomato plants, such as at row ends or garden borders, to intercept pests before they reach the crop.
Borage, which can grow up to three feet tall, should be positioned where it will not shade the tomato plants, which need at least six to eight hours of direct sunlight daily. Flowers that attract beneficial insects, like Sweet Alyssum, can be mass-planted as a groundcover between tomato plants for a continuous nectar source. Avoid planting flowers with aggressive root systems, such as mature dill or sunflowers, too closely, as they will compete with tomato roots for water and nutrients, potentially stunting growth.