Zucchini and Nasturtium
Beneficial Pair — Good Match
Nasturtium's aphid-trapping ability is documented in general, but we aren't aware of a trial confirming it specifically reduces aphid pressure on zucchini's growth tips versus other vegetables. We rate this mixed rather than traditional-lore because the underlying aphid-preference mechanism is real, even without a zucchini-specific study behind it.
Mechanism: Trap Cropping
Nasturtium's documented aphid preference is the mechanism cited here, applied to zucchini's tender new growth tips, which are a common aphid target as the vine expands. This is a more solid application of nasturtium's real trap-crop reputation than the beetle- or borer-deterrent claims sometimes attached to cucurbit pairings, since aphids are genuinely what nasturtium draws - it just isn't specific to zucchini's other major pests like squash bugs or vine borers.
Zucchini and nasturtium are both enthusiastic ground-coverers, which makes this pairing a genuine spatial negotiation rather than a simple companion planting - the two are competing for the same low layer of the bed, not occupying separate niches.
Plan for the Squash's Eventual Size, Not Its Starting Size
A young zucchini transplant looks small enough that nasturtium seems like a fine neighbor at almost any distance, but zucchini's mature spread is considerably larger than its starting footprint, and a nasturtium planted where that spread will eventually reach gets shaded out just as the zucchini's aphid-prone new growth needs it most. Site nasturtium at the true edge of the zucchini's eventual reach, not its current one.
Spacing
This is one pairing where spacing genuinely fights against itself: zucchini needs 24-36 inches to sprawl and nasturtium spreads 8-12 inches of its own, and both are low, ground-covering growth habits competing for the same open soil rather than occupying different layers the way a tall crop and a low one would.
Watch For
By midsummer, an established zucchini plant's broad leaves can outcompete and shade out a nasturtium planted too close, effectively ending whatever trap-crop benefit existed early in the season - plant nasturtium at the outer edge of where the zucchini's mature spread will reach, not directly under where its canopy will eventually sit.
Frequently Asked Questions
Should I plant nasturtium before or after my zucchini?
Slightly before, if possible - nasturtium germinates and establishes quickly, and getting it a head start means it has some size to it by the time zucchini's growth tips are vulnerable to aphids, rather than being immediately overtaken by the faster-growing squash.