Pumpkins and Nasturtium
Beneficial Pair — Good Match
The underlying aphid-preference mechanism is documented, which is why we don't call this traditional lore outright, but we aren't aware of a trial confirming the effect specifically on pumpkin's fast-extending vine tips as opposed to a more contained plant. It's a plausible extension of a real mechanism rather than a directly tested one.
Mechanism: Trap Cropping
Nasturtium's documented aphid preference applies here the same way it does with other cucurbits - drawing aphids away from the tender growing tips of an expanding pumpkin vine. Because a pumpkin vine keeps producing new growth at its leading edge for most of the season as it extends across the garden, there's a longer window where fresh, aphid-vulnerable tissue keeps appearing than with a more compact plant.
Pumpkin vines behave differently from more compact cucurbits like zucchini in a way that matters for this pairing: the plant doesn't just sit and spread outward evenly, it actively extends a leading growth tip across the garden over the course of the season.
A Moving Target, Not a Fixed Border
Because the vulnerable new growth on a pumpkin vine is concentrated at its advancing tip rather than spread evenly across the plant, a nasturtium planted once near the base early on won't stay useful for long - by midseason the vine's growing edge may be several feet away. Gardeners who want to keep this pairing working through the full season generally need to plant nasturtium at intervals along the vine's expected path, or accept that the benefit is mostly front-loaded to early summer.
Spacing
Given how far pumpkin vines eventually travel (48-72 inches from the base plant), nasturtium is more useful planted along the vine's expected path at intervals than as a single fixed border - the vine's growing tip moves over the season, and a nasturtium planting has to be positioned to still be near that tip weeks later.
Watch For
A pumpkin vine will eventually grow past and over any nasturtium planted directly in its path, at which point the nasturtium loses both its light and its usefulness as a trap crop for that section of vine - treat nasturtium plantings near pumpkins as something to refresh or relocate as the vine extends, not a one-time planting.
Frequently Asked Questions
Does a bush-type pumpkin variety avoid this moving-target problem?
Yes, largely - a bush or semi-vining pumpkin variety extends much less over the season than a traditional long-vining type, keeping its growing tips closer to a fixed area rather than traveling several feet from the base plant. A single nasturtium border works better with a bush variety for exactly that reason, even though bush pumpkins are less common than vining types for larger fruit.