Gardens are a labor of love, but destructive pests are unequivically a gardener's bane. Utilize the botanic properties of flowers using companion plantings as part of an integrated pest management plan to minimize insect damage.
One of the benefits attributed to companion planting is the holistic reduction in pest damage. Creating biodiverse gardens of two or more complementary plant species enables nature to minimize garden pests and thereby enables you to cut down on pesticide use. Implementing this organic gardening method, planting flowers with fragrant foliage and blossoms that pests find abhorrent, disorients pests, which in turn protects susceptible plants.
Though enjoyed for their splash of color and beauty in table centerpieces and ornamental gardens, or for artfully dressing up summer salads with edible blooms, marigolds (Tagetes spp.), summer annuals, are especially known for providing natural biological pest control with nematodes. African marigold (Tagetes erecta), Mexican marigold (Targetes minuta) and certain French marigold (Tagete patula) varieties, such as 'Bolero' and 'Scarlet Sophie,' effectively suppress root knot nematodes and other plant-parasitic nematodes.
Biochemical Pest Suppression
African, Mexican and French marigolds are highly allelopathic, which is to say that they produce biochemicals other organisms, micro-organisms or plants find toxic. Alpha-terthienyl is one of the more toxic bioactive compounds produced within marigold roots and tissues and is considered nematocidal, killing nematodes that come into contact with it either through entering the marigold root system or the soil.
Not all marigold varieties deter nematodes. For the varieties that do, none deter all types of nematodes. Determine what type of nematodes you have in your garden and select a marigold variety that is most effective in controlling it.
- Plant marigolds near all vegetable crops to deter aphids, Mexican bean beetles, potato bugs, squash bugs and maggots. It is especially beneficial when interplanted with tomatoes, as it not only helps minimize nematode activity and Mexican bean beetles, but also cuts down on whiteflies and tomato hornworm pests as well.
- Ideally, plant
marigolds two months before planting any other susceptible plant in your garden to effectively reduce nematode damage.
Prized for their versatility in cottage gardens, their showy blooms and their culinary flare in wild flower salads, nasturtiums (Tropaeolum spp.) also serve well as protective, sacrificial plants. This low maintenance, warm-season annual protects muskmelon (Cucumis melo) and watermelon (Citrullus lanatus) when interplanted with radishes (Raphanus sativus) and the perennial tansy (Tancetum vulgare, suited to U.S. Department of Agriculture plant hardiness zones 3 through 8), repelling pests such as the striped cucumber beetle and the spotted cucumber beetle.
Perimeter Trap Crops
Perimeter trap crops protect neighboring plants by luring away destructive insects to sacrificial plants they find more appealing. In the case of aphids, they are drawn to the color yellow. Though aphids are highly attracted to nasturtiums in general, you can capitalize on their color preference by planting yellow-blooming nasturtium varieties at the edge of a garden bed, such as 'Moonlight' (Tropaeolum majus); these sacrificial plants can then be pulled out or locally treated once an infestation is visible.
Though hardy to USDA zones 10 through 11 as a tender perennial, petunias (Petunia spp.) are often grown as annuals. Fragrant, showy blooms come in all colors other than brown and black. When planted with beans, or near tomatoes, petunias repel some aphid varieties, asparagus beetles, Mexican bean beetles, leafhoppers and tomato worms.
From early summer to first frost, dahlias (Dahlia spp., USDA zones 7 through 10) are enjoyed for their lollipop- to dinner-plate-sized blooms in borders, pots or around shrubs. Though considered a hardy winter perennial, performance is best when grown as an annual. As a repellant crop, dahlias repel nematodes.
Beneficial Insect Habitats With Zinnias
Prolifically producing zinnias (Zinnia spp.), which come in a myriad of colors with their daisy-like blooms from summer to fall, are ideal no-fuss flowers. Attracted to the sugary-sweet nectar of this long-blooming annual, ladybugs contentedly do their work in the garden as beneficial predatory insects feeding on destructive garden pests in exchange for the viscous nectar secretions found within zinnia blossoms. Larvae and adults will feed on aphids, mites, scales and the eggs of some insect pests. As long as food and shelter are provided, ladybugs are happy enough to call your garden home and earn their keep.
The attractive foliage and bright blooms of many culinary herbs are not only practical, but pretty, and able to hold their own in any ornamental garden bed. Whether interplanted in a garden or used as a perennial herbal border for visual appeal, common sage (Salvia officinalis, USDA zones 5 to 7) provides an added bonus as a pest repellent for neighboring ornamentals. This compact, shrubby herbaceous perennial is often grown as an annual for its ornamental silvery foliage. Though culinary cooks use sage in savory dishes, when utilized in companion plantings near carrots, tomatoes and cabbage, it also repels carrot flies and cabbage moths.