Kale and Nasturtium
Beneficial Pair — Good Match
Nasturtium's role as an aphid trap crop for brassicas is among the better-supported claims in companion planting, with documented aphid preference for nasturtium foliage over cabbage-family leaves in field conditions. We still note that 'trap crop' means aphids concentrate on the nasturtium rather than disappear - it's a management tool, not an elimination method.
Mechanism: Trap Cropping
Nasturtium is genuinely preferred by black bean aphids and cabbage aphids over most brassica foliage, and when planted as a border or interplant around brassicas like kale, it draws aphid colonies onto itself rather than the crop - this specific host preference has been documented in field observation more thoroughly than most trap-crop claims on this site, which is why kale and nasturtium is one of the stronger pairings we list.
Of the many nasturtium-as-trap-crop pairings across this site, kale and nasturtium sits on firmer ground than most - aphid preference for nasturtium over brassica leaves is genuinely documented, not just repeated folklore.
A Trap Crop Still Needs Managing
It's worth being clear about what 'trap crop' actually means in practice: nasturtium doesn't repel aphids or make them vanish, it concentrates them somewhere other than your kale. Left entirely unchecked for the whole season, a heavily infested nasturtium planting can eventually become a large enough aphid reservoir that some spread back over to nearby brassicas anyway - so periodic removal of the worst-affected nasturtium foliage is part of making this pairing actually work, not an optional extra step.
Spacing
Nasturtium's 8-12 inch spacing works well as a border a foot or two out from a kale row, or interplanted directly between kale plants at their 12-18 inch spacing - either placement puts nasturtium close enough to intercept aphids before they establish on the kale itself.
Watch For
Because nasturtium is deliberately drawing aphid colonies to itself, expect the nasturtium foliage to look genuinely infested over the season - that's the pairing working as intended, not a sign of failure. Check it periodically and remove badly infested leaves or whole plants if aphid numbers get high enough that you're worried about them spreading back to the kale.
Frequently Asked Questions
Does this pairing work as well for a cut-and-come-again kale bed as it does for a one-time head harvest?
It fits a cut-and-come-again bed especially well, since that kind of planting stays in the ground and exposed to aphids for a much longer stretch than a crop harvested once and pulled. That gives the nasturtium border more total season to actually earn its keep, rather than protecting a crop that's only in the ground briefly.