Zucchini and Marigold
Beneficial Pair — Good Match
The claim most commonly made for this pairing - marigold deterring squash bugs and cucumber beetles above ground - lacks controlled evidence, which is why it's filed as traditional lore here. The better-documented marigold mechanism (nematode suppression) applies here too in principle, but it's rarely the reason gardeners actually plant this combination, and we don't want to credit the pairing for a mechanism it isn't usually chosen for.
Mechanism: Trap Cropping
Marigold's most-repeated benefit near zucchini is a general claim that its scent and bright color deter squash bugs and cucumber beetles from finding the crop, which is a very different mechanism from marigold's documented root-based nematode suppression (the effect most solidly established for nightshades like tomatoes and peppers). Zucchini can host root-knot nematodes too, but the above-ground beetle-deterrent claim, which is the one gardeners usually cite for this specific pairing, has much less support behind it.
Marigold shows up around zucchini in garden plans constantly, almost as a default border planting, but it's worth being honest that the specific claim behind it here - beetle and squash bug deterrence - is one of the weaker pieces of marigold folklore in this whole reference.
A Better-Documented Alternative Exists
If cucumber beetles or squash bugs are a serious, recurring problem in your garden, it's worth knowing that agricultural research has identified a genuinely effective trap crop for these specific pests: Blue Hubbard squash planted as a perimeter around the cash crop, which cucumber beetles strongly prefer and concentrate on. Marigold doesn't have that level of documented support for this particular use - it's a reasonable, low-cost border planting, just not a proven beetle solution the way Blue Hubbard is.
Spacing
Marigold's compact 8-12 inch habit makes it a natural border around the outside of a zucchini planting's eventual footprint (24-36 inches) rather than something interplanted directly beneath the squash's broad leaves, where it would be shaded out early.
Watch For
The most effective documented tool against striped and spotted cucumber beetles on squash crops is actually a perimeter trap crop of Blue Hubbard squash, a research-backed technique from cucurbit pest management - worth knowing if beetle pressure is severe enough that you need something more reliable than marigold's border planting.
Frequently Asked Questions
Does the marigold border need to be replanted every year, or can I let it self-seed?
French and signet marigolds, the varieties usually used this way, will self-seed in mild climates, but volunteer seedlings tend to come up scattered rather than in a clean line. Most gardeners still replant intentionally each spring to keep the border positioned precisely around zucchini's expanding footprint rather than wherever seed happened to land the previous fall.