Kale and Mint
Beneficial Pair — Good Match
The scent-masking theory is plausible given how strongly aromatic mint is. No trial we know of has actually measured reduced cabbage moth egg-laying near kale because of a nearby mint planting, though - what's more certain, and arguably the more important fact for this pairing, is what mint's roots will do to your bed if left unchecked - see the spacing note.
Mechanism: Pest Masking (Scent Confusion)
Mint's strong menthol-heavy scent is the reasoning behind this pairing, on the theory that it disrupts cabbage white butterflies and other egg-laying moths from locating kale by smell the way they normally home in on brassica-specific chemical cues. This is the same general scent-masking logic used elsewhere in this reference, applied here to a specific and genuinely troublesome brassica pest rather than a vague general benefit.
Kale and mint is a pairing where the more important thing to know isn't the pest-deterrent theory at all - it's that mint, planted directly in the ground anywhere near kale, will cause a much bigger problem than any aphid or moth ever would.
Get the Scent Benefit Without the Invasion
The fix is straightforward: grow mint in a container, even a large one sunk into the bed with its rim above soil level, positioned close enough to the kale that its scent is still in the air but with its aggressive root system physically blocked from spreading. This preserves whatever unconfirmed pest-masking effect the pairing offers while sidestepping the very real, well-documented problem of mint taking over a shared bed within a single growing season.
Spacing
Never plant mint directly in open ground next to kale - mint spreads aggressively by rhizomes and will invade a kale row within a season, competing hard for root space. Keep mint confined to a buried pot or a physically separated container placed near the kale bed instead, which preserves whatever scent benefit exists without the invasive-root problem.
Watch For
An unconfined mint planting is one of the fastest ways to lose control of a garden bed - its runners spread underground well beyond where the visible plant appears above soil, so even a mint patch that looks contained can already be sending roots into a neighboring kale row.
Frequently Asked Questions
Does a container-grown mint lose the scent-masking benefit if it's a few feet away rather than right next to kale?
Possibly some, though the pest claim itself is unconfirmed either way, so there's no established minimum distance to worry about losing. A containerized mint placed close enough that you can smell it standing next to the kale bed is a reasonable middle ground - near enough to plausibly offer whatever scent effect exists, without needing to sit right against the kale row.