Pumpkins and Marigold
Beneficial Pair — Good Match
The squash-bug and cucumber-beetle deterrent claim is unconfirmed folklore, the same as it is for marigold near other cucurbits. What's different about pumpkins specifically is that the practical decision - where exactly to put the border relative to a vine that will eventually stretch far beyond its starting point - matters more here than the underlying evidence question.
Mechanism: Trap Cropping
Marigold's claimed benefit here follows the familiar folk reasoning applied to squash-family crops generally - scent or color discouraging squash bugs and cucumber beetles - but pumpkins raise a different practical question than most cucurbits do: a pumpkin hill is usually one planting for the whole 90-120 day season, with a single vine eventually running 6 feet or more from where it started, so the marigold border isn't a decision you revisit every week the way you would with a crop you're walking through constantly to pick.
Pumpkins grow differently from most of the cucurbits marigold gets paired with on this site - fewer plants, a longer single season, and a vine that keeps extending well past where the plant first went in the ground, which changes what "planning the border" actually means here.
A One-Time Decision for a Vine That Keeps Moving
Because you're not replanting or repeatedly walking through a pumpkin hill the way you would a crop picked every few days, the marigold border is essentially a single decision made at planting time and left alone - which makes it more important to get the placement right up front. The real risk isn't choosing the wrong flower; it's underestimating how far a single pumpkin vine will travel by the end of the season and placing marigold somewhere the vine simply engulfs by late summer, well before harvest.
Spacing
Set the marigold border well outside a pumpkin hill's full eventual footprint from the start, not just its current size - pumpkins' 48-72 inch spread is measured from the base plant, but an individual vine can travel considerably farther than that over the season, so a border that looks generously distant in June can end up under the vine's leaves by September.
Watch For
Because a pumpkin hill is typically planted once and left for the whole season rather than replanted or heavily walked through the way a continuously-picked crop is, this is a set-it-and-largely-forget-it border decision - the main thing worth revisiting partway through summer is whether the vine's actual growth has outpaced where you expected it to reach when you first planted the marigold.
Frequently Asked Questions
Do I need to move or replant marigold partway through a pumpkin's season?
Not usually - since a pumpkin hill is normally a single season-long planting, get the border distance right from the start based on the vine's expected full reach rather than planning to adjust it later, since access to do so gets harder once the vine has sprawled.