Natural pest control (NPC) uses plants, beneficial insects, and cultural practices to manage garden pests without relying on synthetic chemicals. Flowers are a highly effective component of this strategy. These flowering plants protect crops by releasing volatile compounds that confuse or repel harmful insects or by containing natural toxins. Understanding how different flowers function allows for the precise and intentional placement necessary to create a healthy, naturally defended garden.
Flowers That Deter Pests Through Scent and Oils
Many flowers create a protective buffer in the garden by emitting powerful aromatic compounds that mask the scent of vulnerable plants. Insects often rely on smell to locate their host plants, and strong floral oils can confuse this process, deterring pests from landing. These repellent flowers are useful for companion planting, where they are interspersed among food crops to provide an aromatic camouflage.
French Marigolds (Tagetes patula) are particularly well-known for their dual-action defense against a variety of pests. Above ground, the flowers and foliage release thiophenes and limonene that confuse and repel whiteflies and aphids. Below the soil surface, the roots exude alpha-terthienyl, a chemical that is highly toxic to root-knot nematodes, microscopic roundworms that feed on plant roots. This below-ground action can effectively reduce nematode populations in the soil when Marigolds are planted a few months before host crops.
Nasturtiums (Tropaeolum majus) serve two distinct roles in pest management: repellant and trap crop. Their peppery foliage is thought to repel squash bugs and cabbage worms from nearby vegetables. As a sacrificial plant, aphids and cabbage white butterflies find Nasturtiums highly attractive. The pest is drawn to the Nasturtium, sparing more valuable crops like cabbage or tomatoes.
Lavender (Lavandula) offers a long-lasting perimeter defense due to its high concentration of aromatic compounds. The strong, pleasant scent is derived from linalool and camphor, which disrupt the olfactory receptors of many common garden pests. Moths, mosquitoes, and fleas are particularly sensitive to this fragrance, making Lavender effective for planting near entryways or seating areas.
Flowers Containing Natural Insect-Killing Compounds
Some flowers contain compounds that are not merely deterrents but are natural insecticides. The most prominent example comes from the Chrysanthemum genus, specifically the Dalmatian daisy (Chrysanthemum cinerariifolium). The flower heads of this plant are the natural source of a group of compounds called pyrethrins.
Pyrethrins are a mixture of six related esters that are potent neurotoxins to insects. They work by binding to the voltage-gated sodium channels in the insect’s nerve cells, preventing the channels from closing properly. This prolonged opening causes a continuous, uncontrolled firing of nerve signals, leading to rapid paralysis. This active ingredient is a popular organic control because it degrades quickly in sunlight, minimizing residual environmental impact.
Pyrethrins served as the chemical blueprint for the creation of synthetic versions called pyrethroids. While pyrethroids are engineered to be more stable and longer-lasting, the natural pyrethrins are favored in organic gardening due to their rapid breakdown. The flower itself can be dried and crushed to create a powder, or the extract can be used in sprays to target soft-bodied insects like aphids, thrips, and whiteflies.
Strategic Placement for Maximum Protection
Effective natural pest control relies on the proper placement of these beneficial flowers to maximize their biochemical effects. The choice of planting technique depends on whether the flower is intended to be a general repellent, a specific soil treatment, or a sacrificial trap.
For managing soil-dwelling pests like root-knot nematodes, French Marigolds should be planted densely in the problem area, ideally as a cover crop for a full season before the main crop is introduced. When interplanting Marigolds with tomatoes to repel whiteflies, creating a border around the entire crop is more effective than interspersing individual plants, as this concentrates the volatile compounds. A perimeter planting of a strong-scented flower like Lavender can create a sensory barrier against flying pests like moths and mosquitoes.
The strategy of “trap cropping” requires purposeful placement of the sacrificial flower away from the target crop. Nasturtiums should be planted far enough from vulnerable crops like cabbage to intercept the pests, but close enough to lure them. Once the Nasturtiums are heavily infested with pests like aphids, the entire plant can be removed and disposed of before the pests spread to the main garden.