Aphids top the list of nasturtium pests, often colonizing stems and flower buds in dense clusters that seem to appear overnight. Caterpillars, flea beetles, slugs, and whiteflies round out the usual lineup, though the severity of each depends on your climate and what else is growing nearby. Nasturtiums occupy an unusual niche in the garden: they attract certain pests so reliably that gardeners sometimes plant them on purpose as sacrificial decoys, which means managing these insects is less about eradication and more about deciding how much damage you can tolerate and where you want the pests to congregate.
Aphids Are the Headliner
If you grow nasturtiums long enough, you will meet aphids. Black bean aphids and green peach aphids are the most frequent visitors, though several species show up depending on geography. The black aphids you see massed on nasturtium stems are not always the same species as the black bean aphid found on broad beans and other crops. Research in Canada found that aphid cultures from one region thrived on nasturtium but could not survive on faba bean, while cultures from another region did the opposite, suggesting these are biologically distinct species despite looking nearly identical.1The Canadian Entomologist. Studies on Two Species of Black Aphids (Homoptera: Aphididae) on Faba Bean and Nasturtium Earlier work confirmed that a black aphid species living on nasturtium would land on faba bean and attempt to feed, yet consistently failed to take up sap and died, along with any offspring.2Entomologia Experimentalis et Applicata. Abortive Feeding Behaviour in a Black Aphid of the Aphis Fabae Group
Why does this matter for a gardener? It means the aphids colonizing your nasturtiums may not be the same ones that would attack your beans or brassicas. The common advice to plant nasturtiums as an aphid “trap crop” assumes the pests will leave other plants alone if nasturtiums are available. That works in some situations, but if the aphid species on nasturtium is host-specific, it was never going to infest your vegetables in the first place. The trap-crop strategy is most effective for generalist aphids like the green peach aphid, which feeds on hundreds of plant species and genuinely might choose the nasturtium over your lettuce.
Signs of an Aphid Problem
Aphids cluster on the undersides of leaves, around tender new growth, and along flower stems. You will notice curling or yellowing leaves, a sticky residue called honeydew on foliage below the colony, and sometimes a black sooty mold that grows on the honeydew. Ants trailing up the stems are another giveaway, since ants farm aphids for the honeydew and will actively protect them from predators.
Dealing With Aphids on Nasturtiums
A strong jet of water from a hose knocks aphids off the plant and kills a significant number of them. Repeat every few days during an active infestation. Soft-bodied insects like aphids are poor climbers once dislodged, so many never make it back. For heavier infestations, insecticidal soap or neem oil sprays work on contact. Coat the undersides of leaves thoroughly, since that is where aphids hide. If ants are protecting the colony, a band of sticky barrier product around the base of nearby structures or stakes can disrupt the ant highway and let predatory insects do their work.
Ladybugs, lacewing larvae, and hoverfly larvae are voracious aphid predators. A single lacewing larva can eat several hundred aphids during its development. Encouraging these insects by planting small-flowered herbs and wildflowers nearby often keeps aphid populations in check without any spraying. If your nasturtiums are purely decorative and the infestation is severe, pulling out the worst-affected plants and composting them is sometimes the most practical option.
Caterpillars From Cabbage Butterflies
Nasturtiums belong to the family Tropaeolaceae and produce glucosinolates, the same pungent sulfur compounds found in cabbages, mustard, and radishes. That chemical kinship makes nasturtiums attractive to the same caterpillars that devour brassica crops. The cabbage white butterfly, Pieris rapae, readily lays eggs on nasturtium, and the hatching larvae feed normally and develop into healthy pupae and adults.3PubMed. Rejection of Host Plant by Larvae of Cabbage Butterfly: Diet-Dependent Sensitivity to an Antifeedant The larger cabbage white, Pieris brassicae, also uses nasturtium as a host, though it grows more slowly on nasturtium than on Brussels sprouts or turnip.4Entomologia Experimentalis et Applicata. Interactions Among Three Trophic Levels: The Influence of Host Plant on Performance of Pieris brassicae and Its Parasitoid, Cotesia glomerata
You will spot caterpillar damage as ragged holes chewed through leaves, often starting at the edges. The green larvae of the small cabbage white blend in surprisingly well against nasturtium foliage, so look carefully along leaf veins and on the undersides. Frass, the dark pellets of caterpillar droppings, on lower leaves is another clue.
Hand-picking is the simplest control. Check plants every couple of days and remove caterpillars by hand. For larger plantings, a spray containing Bacillus thuringiensis (Bt), a naturally occurring soil bacterium, kills caterpillars that ingest treated foliage without harming bees, ladybugs, or other beneficial insects. Bt breaks down in sunlight within a few days, so reapply after rain or every week during peak butterfly season. Floating row cover draped over the plants physically blocks egg-laying adults, though this sacrifices the flowers’ ornamental appeal and prevents pollinators from visiting.
Flea Beetles
Flea beetles are tiny, dark, shiny beetles that jump when disturbed. They chew small round holes in nasturtium leaves, giving the foliage a “shotgun” appearance. Several species feed on plants in the Brassicaceae and Tropaeolaceae families, so nasturtiums catch their attention for the same glucosinolate reason that attracts cabbage whites. Damage is mostly cosmetic on mature plants, but heavy feeding on seedlings can stunt or kill young nasturtiums before they get established.
Yellow sticky traps placed near the base of plants catch adult flea beetles. Diatomaceous earth dusted on dry foliage damages the insects’ waxy cuticle and dehydrates them, though you need to reapply after watering or rain. Healthy, fast-growing nasturtiums usually outrun flea beetle damage once they get past the seedling stage, so the most effective strategy is often just getting the plants established quickly. Starting seeds indoors and transplanting larger seedlings outdoors reduces the window when plants are most vulnerable.
Whiteflies
Whiteflies are tiny, white-winged insects that rise in a cloud when you brush against an infested plant. Like aphids, they feed on plant sap, excrete honeydew, and congregate on leaf undersides. Nasturtiums in greenhouses or in warm, humid climates are most vulnerable. Outdoor nasturtiums in temperate regions see whiteflies less frequently because wind and natural predators keep populations lower.
Yellow sticky cards hung among the plants trap adults effectively. Insecticidal soap sprays kill whiteflies on contact but need thorough coverage and repeated applications because the eggs and pupae attached to leaves are harder to reach. Encarsia formosa, a tiny parasitoid wasp commercially available for greenhouse use, is one of the most effective biological controls for whitefly. If you grow nasturtiums in a greenhouse or conservatory, introducing these wasps early in the season can prevent whitefly populations from building to damaging levels.
Slugs and Snails
Nasturtium seedlings are slug magnets. The soft, succulent stems and rounded leaves are easy for slugs and snails to consume, and a single night of feeding can level a row of young plants. Mature nasturtiums hold up better because they grow quickly and produce more foliage than slugs can eat, but in wet climates or during prolonged rainy spells the damage can remain significant.
Beer traps, copper tape around containers, and evening hand-picking all reduce slug numbers. Iron phosphate pellets are a widely available slug bait that breaks down into compounds naturally present in soil, making them a lower-risk option than older metaldehyde-based baits. Watering in the morning rather than the evening helps too, since dry soil surfaces at night give slugs less incentive to travel across your beds. Raised containers and hanging baskets sidestep the slug problem almost entirely, and nasturtiums happen to trail beautifully from both.
Nasturtiums as a Deliberate Trap Crop
Many gardeners plant nasturtiums around vegetable beds specifically to lure aphids and caterpillars away from crops. The logic is straightforward: if pests prefer nasturtiums, they will settle there instead of on your kale or tomatoes. For generalist aphids, this strategy has some merit, especially when the nasturtiums are planted a few weeks before the main crop so the trap plants are already established and attractive when winged aphids arrive. The key is to monitor the trap plants and remove or treat them before aphid populations explode and start sending winged migrants elsewhere in the garden.
For caterpillars, the picture is more nuanced. Cabbage whites lay eggs on nasturtiums, but they also lay eggs on your brassicas. Having nasturtiums nearby does not guarantee the butterflies will ignore your cabbage. What nasturtiums do offer is an easy scouting location: if you see caterpillar eggs or early-instar larvae on nasturtium leaves, you know the butterflies are active and it is time to check your brassicas too. Think of them as an early warning system rather than a foolproof shield.
Natural Enemies Worth Encouraging
The parasitoid wasp Cotesia glomerata lays its eggs inside living caterpillars of cabbage white butterflies. The wasp larvae develop inside the caterpillar, eventually killing it and spinning small yellow cocoons on or near the host’s body. Research on how host-plant choice affects this three-way relationship found something counterintuitive: while caterpillars grew more slowly on nasturtium compared to brassica crops, the parasitoid wasps that emerged from nasturtium-fed caterpillars actually developed faster and lived longer than those from caterpillars reared on Brussels sprouts.4Entomologia Experimentalis et Applicata. Interactions Among Three Trophic Levels: The Influence of Host Plant on Performance of Pieris brassicae and Its Parasitoid, Cotesia glomerata In other words, nasturtiums seem to make the caterpillar’s body a better environment for its own killer. That finding suggests nasturtiums in the garden may indirectly boost biological control of cabbage whites, even beyond any trap-crop effect.
Beyond parasitoid wasps, ground beetles, spiders, hoverflies, and birds all feed on nasturtium pests. Leaving some leaf litter and low ground cover near your nasturtium beds gives ground beetles somewhere to shelter. Allowing a few umbelliferous plants like dill, fennel, or parsley to flower nearby provides nectar for adult hoverflies, whose larvae are dedicated aphid predators. A garden that supports a diversity of these predators rarely has pest problems severe enough to require chemical intervention.
When Pests Are Worse Than Usual
Certain conditions amplify nasturtium pest problems. Overly rich, high-nitrogen soil produces lush, soft growth that aphids find irresistible. Nasturtiums actually flower more prolifically in lean soil, so cutting back on fertilizer can reduce pest pressure and improve the display at the same time. Crowded plantings with poor air circulation create a humid microclimate that favors whiteflies and fungal diseases, which often follow insect damage. Spacing plants generously and growing them where they get good airflow helps on both fronts.
Drought-stressed nasturtiums sometimes attract spider mites, especially in hot, dry summers. Spider mites are almost invisible to the naked eye but leave fine webbing on the undersides of leaves and cause a stippled, bronzed appearance on the upper surface. A strong water spray aimed at the leaf undersides disrupts their webbing and knocks them off. If mite damage is severe, horticultural oil or insecticidal soap applied in the cooler hours of the day can bring things under control. Avoid broad-spectrum insecticides, which kill the predatory mites and other beneficial insects that normally keep spider mite populations in check, often making the problem worse in the long run.
Eating Nasturtiums Safely Despite the Bugs
Nasturtium leaves, flowers, and unripe seed pods are all edible, with a peppery flavor similar to watercress. If you plan to eat them, pest management becomes more personal. Any spray residue, even from organic-approved products like neem oil or insecticidal soap, should be washed off thoroughly or, better yet, avoided on the parts you plan to harvest. Hand-picking pests and using water sprays are the cleanest options for edible nasturtiums.
Inspect harvested flowers and leaves carefully. Aphids hide inside the trumpet-shaped flowers and between overlapping petals. Soaking flowers in cold salted water for ten to fifteen minutes encourages hidden insects to float out. Give everything a gentle rinse and pat dry before using. Caterpillar frass on leaves is harmless but unappetizing; a quick wash takes care of it. Growing nasturtiums in containers on a balcony or patio, away from heavy garden pest populations, tends to produce the cleanest harvest with the least effort.
Varieties and Their Relative Vulnerability
Not all nasturtium varieties attract pests equally. The trailing types with large, open-habit growth tend to suffer more from aphids, partly because their dense foliage creates sheltered microclimates that aphids appreciate. Compact bush varieties like ‘Alaska’ or ‘Jewel Mix’ have a more open structure that is easier to monitor and allows better airflow. Varieties with darker foliage sometimes seem to attract fewer flea beetles than pale-leaved types, though this varies by region and has not been studied rigorously enough to count on.
Canary creeper (Tropaeolum peregrinum), a related climbing species sometimes grouped with nasturtiums in garden catalogs, has its own pest profile. It attracts cabbage whites like the common nasturtium does, but its vigorous vertical growth means slug damage is usually limited to the lowest leaves. If you want nasturtium-family flowers with fewer ground-level pest headaches, training a canary creeper up a trellis keeps much of the foliage out of slug range while still providing habitat for beneficial insects higher up.