Companion planting is a gardening technique where different species are grown near one another to provide mutual benefits, often serving as a natural form of pest management. This strategy utilizes the natural properties of certain plants, such as strong scents or physical structures, to protect a primary crop from insect damage. When growing potatoes, the goal of this interplanting is to deter or confuse the insects that specifically target the foliage and tubers, reducing the need for chemical interventions.
Key Pests That Target Potatoes
Potato plants are vulnerable to a few insect species that can cause significant damage to both the leaves and the developing tubers underground. The Colorado Potato Beetle (Leptinotarsa decemlineata) is perhaps the most serious threat, with both the adults and their reddish-orange larvae causing rapid and severe defoliation of the plants. This feeding activity can quickly stunt growth and drastically reduce the final yield of potatoes.
Flea beetles (Epitrix spp.) are also problematic, as the adults chew small, round “shot holes” in the leaves, while their larvae feed on the tubers, creating tiny tunnels or scars just beneath the skin. Aphids are sap-sucking insects that cause leaf distortion and can transmit viral diseases, like Potato Virus Y, which is often a greater concern than their direct feeding damage. Understanding these specific threats helps explain why particular companion plants are effective deterrents.
Companion Plants That Act as Chemical Repellents
Many aromatic herbs and flowers can protect potatoes by releasing volatile organic compounds that confuse or repel insect pests. This mechanism works either by masking the scent of the potato plant, making it difficult for pests to locate, or by producing compounds that are directly noxious to the insects. These chemical deterrents are most effective when planted close to the potato rows.
French marigolds (Tagetes patula) are highly regarded for their pest-repellent properties, particularly against the Colorado Potato Beetle. The roots of certain varieties release thiopene, which suppresses nematodes, while the strong scent of the foliage deters adult beetles from landing and laying eggs. Planting marigolds every few feet between the potato plants or along the perimeter of the patch is a common strategy.
Catnip (Nepeta cataria) is another potent repellent due to its high concentration of nepetalactone, an essential oil that is particularly disliked by the Colorado Potato Beetle, flea beetles, and aphids. Interplanting catnip near the potato hills creates a strong aromatic barrier that helps disrupt the pests’ ability to find their host plant.
Members of the Allium family, such as garlic and chives, release sulfur compounds that create a generalized repellent effect. The pungent odor of chives, when planted as a border or interspersed throughout the rows, helps to deter aphids and spider mites from establishing colonies on the potato foliage. Tansy is an herb that contains camphor and thujone, which acts as a strong deterrent against the Colorado Potato Beetle and flying aphids. While effective, tansy should be managed carefully due to its vigorous growth habit, often being reserved for planting at the edges of the garden area.
Strategies Using Trap Crops and Physical Barriers
Beyond chemical repellency, companion planting can employ physical strategies, such as using specific plants to distract pests or to obstruct their movement. Trap cropping involves planting a preferred host species nearby to lure pests away from the main crop, concentrating the infestation where it can be easily managed or destroyed. Nasturtiums are a classic example, as they are highly attractive to aphids and certain beetles, drawing them away from the potato foliage.
The bright flowers and tender leaves of nasturtiums act as a decoy, becoming the primary feeding site for pests like aphids, which can then be removed manually or treated without harming the potato plants. This diversion tactic relies on placing the trap crop a short distance away from the potato rows to intercept the pests.
Plants that grow tall and dense can also serve as physical barriers, confusing flying insects and obstructing their direct flight paths to the potato crop. Bush beans or corn, for instance, are often grown alongside potatoes; the height of the corn creates a windbreak and a visual obstruction that can confuse some potato pests. Bush beans, in particular, are a good choice because they do not compete heavily for the underground space needed by the potato tubers.
The presence of these taller plants disrupts the visual and chemical signals pests use to locate a large patch of a single host crop. This mixed planting strategy mimics a more natural, biodiverse environment, making it harder for pests to find and infest the potato plants effectively. The timing of planting these barrier crops is important to ensure they reach a sufficient height when the potato foliage is most vulnerable to attack.