Cabbage and Nasturtium
Beneficial Pair — Good Match
Evidence-backed - both the cabbage white butterfly preference and nasturtium's broader aphid-trapping role are documented in trap-cropping research specific to brassica pest management, not just general companion-planting tradition. This is one of the stronger evidence pairings on this site.
Mechanism: Trap Cropping
Cabbage white butterfly (Pieris rapae), whose caterpillars are one of cabbage's most persistent pests, shows a documented feeding and egg-laying preference for nasturtium over brassica crops when both are available, and field research on trap cropping has specifically used nasturtium to draw this pest away from cabbage and related crops with measurable results. Nasturtium is also a strong aphid trap crop generally, adding a secondary benefit against the aphid species that also trouble cabbage.
Cabbage white butterfly is the caterpillar pest most gardeners battle on cabbage, and nasturtium's documented preference as an alternative host makes this one of the better-supported trap-cropping pairings on this site.
A Documented Preference, Not Just a Guess
Cabbage white butterflies lay their eggs preferentially based on both visual and chemical cues from host plants, and research into brassica pest management has found nasturtium to be a genuinely attractive alternative for egg-laying compared to cabbage itself under certain conditions - which is the basis for using it deliberately as a trap crop rather than an accidental side benefit. Combined with nasturtium's separately well-documented role as an aphid magnet, a nasturtium border gives a cabbage bed protection against two of its more common pest pressures through the same planting.
Perimeter Placement Matters More Here Than for Most Pairings
Because the mechanism depends on intercepting pests as they arrive rather than simply coexisting nearby, where you put the nasturtium changes how well it works. A ring or border planting around the cabbage bed's edges puts nasturtium in the path of butterflies and aphids approaching from any direction, which is more effective than a few plants tucked randomly among the cabbage itself. This is a small but meaningful difference from most beneficial pairings on this site, where exact placement within the bed matters less than simple proximity.
Monitoring Is Part of the Deal
As with nasturtium's other trap-crop roles on this site, this pairing requires actual attention through the season rather than a plant-and-forget approach. A nasturtium border that's become heavily colonized with aphids or caterpillars is still doing its job of drawing pests away from the cabbage, but it can eventually become crowded enough that pests spill over onto the crop it was meant to protect. Checking the nasturtium weekly and cutting back the worst-affected growth keeps the trap crop working as intended rather than turning into a reservoir.
A Reasonable Companion for Other Brassicas, Too
Because cabbage white butterfly and aphids trouble brassicas broadly rather than cabbage specifically, the same border-planting approach extends to broccoli, kale, and Brussels sprouts beds without needing to change the underlying logic. If you're planning a mixed brassica section of the garden, a single nasturtium border around the whole area can serve all of the brassica crops in it rather than needing a separate ring for each.
Spacing
Plant nasturtium at the border of the cabbage bed rather than directly interspersed, roughly 12-18 inches out - the trap crop works by intercepting egg-laying butterflies and aphids as they approach, which a perimeter planting does more effectively than scattering a few plants deep inside the bed.
Watch For
Like any trap crop, nasturtium needs monitoring rather than being planted and forgotten - check it regularly for cabbage white caterpillars and aphid colonies, and be ready to remove heavily infested foliage so the trap crop doesn't become a launching point for pests to spread onto the cabbage once it's fully colonized. Cabbage white butterflies are also strong fliers and won't be stopped entirely by a nasturtium border, so this pairing reduces pressure rather than eliminating the need to check cabbage directly for caterpillars and their pale yellow egg clusters.
Frequently Asked Questions
If cabbage white butterfly isn't a big problem in my area, is a nasturtium border still worth planting?
Yes - aphid pressure is the more geographically universal of this pairing's two benefits. Cabbage white activity varies a fair amount by region and season, but aphids show up in nearly every vegetable garden, so a nasturtium border still earns its space through aphid interception even somewhere the butterfly is rarely an issue.
Does nasturtium need to fully surround the cabbage bed to work?
A full border is more effective than scattered plants, but even a partial border on the side facing prevailing wind or the most pest pressure in your area provides some benefit - a complete ring simply covers more approach directions.