Radishes and Sweet Corn
Beneficial Pair — Good Match
The timing logic here is sound and low-risk, though we haven't come across a study that measured an actual yield or weed-suppression benefit from interplanting radishes specifically with sweet corn, as opposed to simply mulching the bare soil directly. It's a reasonable way to use otherwise-idle space rather than a proven yield-boosting technique.
Mechanism: Living Mulch
Sweet corn is notably slow to establish real ground cover of its own - young corn seedlings stay narrow and widely spaced for weeks before the canopy fills in - leaving bare soil exposed to sun and weeds during that window. Radishes, sown at the same time in the gaps between corn rows, germinate and mature fast enough to cover that soil and be harvested and gone well before the corn needs the space for its own root system.
Sweet corn spends its first several weeks as a collection of narrow, widely-spaced seedlings, which leaves a lot of exposed soil between rows for far longer than most vegetable gardeners are used to tolerating - radishes are one of the more practical ways to put that early-season gap to use.
A Fast Crop for a Slow Starter
Because radishes mature in as little as 22-30 days - a fraction of sweet corn's 60-100 day season - they're harvested and out of the way long before the corn's canopy or root system needs that space for itself. This makes the pairing more of a smart succession-in-place than a season-long companionship, similar in spirit to how fast crops are often tucked into the early weeks of any slow-starting main crop.
Spacing
Sweet corn's 12-18 inch spacing between plants leaves real gaps early in the season - sow radishes at their normal 2-3 inch spacing into those gaps between corn seedlings, and expect to harvest the radishes well before corn stalks are tall enough to shade the ground beneath them.
Watch For
Corn's root system spreads wide as the stalks mature, so radishes need to be fully harvested before corn roots fill in that space - leaving radishes too long risks disturbing developing corn roots when you finally go to pull them.
Frequently Asked Questions
Will radishes compete with young corn seedlings for water?
Minimally, if harvested on schedule - radishes are shallow-rooted and mature quickly, so as long as you pull them within their normal timeframe rather than leaving them to bolt, they're gone before corn's water needs increase significantly.