Nasturtiums are vibrant annual flowers, recognized for their lily-pad-like leaves and peppery-tasting, edible blooms. This easy-to-grow plant is also a celebrated component of natural gardening, known for its powerful interactions with nearby vegetation. Companion planting with nasturtiums is a technique that uses the plant’s unique properties to manage garden health and improve yields. They are valued primarily for the strategic role they play in protecting other plants.
Protective Companions: Deterring Pests
Nasturtiums function as a protective companion by emitting volatile organic compounds that repel specific insect species. The plant’s distinct, pungent aroma can confuse or mask the scent of desired crops, making it difficult for certain pests to locate their target. This protective mechanism is effective against insects that rely heavily on scent to find host plants.
Planting nasturtiums near cucurbit crops, such as squash and zucchini, helps to deter damaging pests like the squash bug and the cucumber beetle. Their presence near tomatoes or peppers provides a similar buffer against whiteflies. The strong scent also helps to discourage cabbage moths from laying eggs on brassicas, reducing the number of destructive cabbage worms. This strategy of deterrence works best when nasturtiums are interplanted throughout the garden to create a broad protective barrier.
The Strategy of Trap Cropping
The strategic use of nasturtiums as a trap crop is fundamentally different from simple deterrence, relying on attraction rather than repulsion. Trap cropping exploits the nasturtium’s highly appealing nature to certain insect populations, luring them away from high-value food crops. The plant serves as a sacrificial host, concentrating pests onto its leaves and stems where they can be managed.
Aphids, in particular, find the tender foliage of nasturtiums irresistible and will colonize them rapidly, preferring them over plants like kale or broccoli. This concentrated infestation can then be controlled by removing the heavily affected nasturtium plants or by treating them with a targeted, non-toxic spray. For this strategy to be successful, the nasturtiums must be planted close enough to the main crops to draw the pests, but far enough away to prevent pests from easily migrating once the trap crop is full.
A practical approach is to position the nasturtiums on the perimeter of the garden bed or slightly away from the main planting area. This placement ensures they act as the initial point of contact for incoming pests, diverting the bulk of the population before they reach the vegetables. By monitoring the trap crop closely and intervening when the infestation becomes heavy, gardeners can significantly reduce the overall pest pressure on their primary harvest.
Negative Pairings to Avoid
While nasturtiums are beneficial companions for many plants, some pairings can be counterproductive due to competition or shared vulnerabilities. Avoid planting nasturtiums near plants that are heavy feeders, such as potatoes, as both will compete intensely for soil nutrients and moisture. Nasturtiums prefer poorer soil conditions, and the competition can stunt the growth of both the flower and the vegetable.
Another poor pairing involves certain herbs like fennel, which is known to be allelopathic. Fennel releases chemical compounds into the soil that inhibit the growth of many neighboring plants, including nasturtiums. Furthermore, while nasturtiums can be a trap crop for aphids, they can also attract the blackfly, which is highly detrimental to beans. To prevent the blackfly from devastating a bean crop, nasturtiums should be planted at least three feet away.