Tomatoes and Sweet Corn
Antagonist Pair — Keep Apart
Mixed rather than clearly evidence-backed: nutrient competition between heavy feeders is real agronomy but not unique to corn and tomatoes specifically - any two nitrogen-hungry crops crowded together compete the same way. The shared-pest angle (corn earworm/tomato fruitworm being the same species) is a documented entomological fact, but how much practical difference proximity makes to infestation rates in a home garden hasn't been isolated in a controlled trial we're aware of.
Mechanism: Nutrient Competition
Both crops are genuinely heavy nitrogen feeders, so planting them close together in thin soil does mean real competition for the same nutrient pool - though that's true of almost any two heavy feeders grown tightly together, not something specific to this pairing. The more distinctive concern is Helicoverpa zea, a single insect species known as corn earworm on corn and tomato fruitworm on tomato - the same caterpillar that bores into corn ears will just as happily bore into tomato fruit, so a heavy infestation on one crop is a direct threat to the other nearby.
This pairing gets filed as an antagonist mostly on general "they're both hungry crops" grounds, but the more specific and more interesting reason to keep them apart is a single insect that goes by two different names depending on which plant it's eating.
One Caterpillar, Two Crops
Corn earworm and tomato fruitworm are the same species, Helicoverpa zea, just named for whichever crop it happens to be damaging at the time. The moth lays eggs on both corn silks and tomato foliage, and the resulting caterpillar bores into corn ears or tomato fruit with equal enthusiasm. Growing the two crops side by side doesn't create this pest - it's a serious problem for each crop independently across most of North America - but it does mean a population that builds up on one is sitting right next to the other host, rather than needing to travel any distance to find it.
The Nutrient Story Is Real But Generic
Sweet corn and tomatoes are both classified as heavy feeders, drawing significantly on soil nitrogen through their growing season, and packed close together in a bed that isn't generously fed, they will compete for it. That's a genuine agronomic consideration, but it's worth being honest that it applies to plenty of other heavy-feeder pairings too - it's not a specific chemical or biological interaction unique to corn and tomatoes the way, say, fennel's allelopathy is unique to fennel. Well-amended soil and adequate spacing address most of this concern regardless of what else is nearby.
The height difference matters as much as either of the above in practice: a stand of sweet corn casts real shade by midsummer, and a tomato plant crowded up against it will get measurably less direct light through the afternoon, which affects fruiting more directly than a shared nutrient pool does. If you're tight on space, put the tomato on the sunnier, unshaded side and give both crops enough room that neither is drawing hard on the same few square feet of soil.
Spacing
Give this pairing real separation if you can - at least 3-4 feet - both because sweet corn's tall, dense stand will shade a tomato plant for much of the day, and because tomatoes want the deep, even watering that corn's shallower, wider root mat tends to pull moisture away from in tight quarters.
Watch For
Watch for the classic sign of corn earworm/tomato fruitworm damage - a small entry hole with frass (insect droppings) near it, on either the corn ear tip or the tomato fruit - and treat it as the same pest problem regardless of which crop you find it on first. Corn's height also means it will genuinely shade a nearby tomato as it matures, which is a bigger practical issue for tomato fruiting than any nutrient competition.
Frequently Asked Questions
Does the shared-pest risk apply all season, or are there safer windows to plant these two near each other?
Moth activity isn't constant through the season - egg-laying pressure tends to peak around when corn is silking, since that's what the moths are drawn to lay on first. Many local extension services track regional moth flight activity through pheromone traps, and timing your corn planting so silking falls outside the heaviest local flight window (often mid-to-late summer in a lot of regions) can reduce pressure on both crops more than spacing alone.
Is it just tomatoes that share this pest with corn, or are other nightshades at risk too?
The same species affects peppers as well, sometimes informally called pepper fruitworm damage, so a pepper bed near a heavily infested corn planting carries a similar risk profile to a nearby tomato bed. Eggplant is a less commonly reported host but belongs to the same nightshade family, so it's worth checking if you notice a heavy earworm year and have eggplant planted nearby too.