Sweet Corn and Lima Beans
Beneficial Pair — Good Match
Nitrogen fixation by legumes is well established, and the fact that lima beans and corn actually overlap in season (unlike peas and corn) makes the mechanism more directly applicable here. Even so, the amount of nitrogen genuinely shared with a neighboring plant while the legume is still actively growing - as opposed to after it's tilled in - remains a smaller, less-quantified effect than the fixation process itself.
Mechanism: Nitrogen Fixing
Lima beans fix nitrogen through root nodule bacteria the same way other legumes do, but unlike peas, they're a genuinely warm-season, frost-tender crop that shares sweet corn's actual growing window rather than finishing before it starts - which makes the two truly simultaneous companions rather than a succession pairing, and gives sweet corn's demanding nitrogen appetite a live nitrogen-fixing neighbor for its full season rather than just residual nitrogen left behind by an earlier crop.
Lima beans solve the timing problem that undercuts the peas-and-corn pairing elsewhere on this site: both are frost-tender, warm-season crops with genuinely overlapping growing windows, so this is one of the few nitrogen-fixing legume pairings with sweet corn that actually functions as simultaneous companions rather than a spring-then-summer succession.
Bush Varieties Fit This Pairing Better Than Pole
Because sweet corn varieties bred for eating fresh aren't typically selected for the sturdy stalk strength that historical three sisters corn varieties offered, a climbing pole lima bean can genuinely stress a corn stalk not built to support it. A bush lima variety planted between corn rows gets the same season-long nitrogen-fixing benefit without asking the corn to double as a trellis.
Spacing
Lima beans want 4-6 inches and sweet corn 12-18, close enough that a bush lima variety can be interplanted between corn rows without either crop's spacing being seriously compromised, unlike the pole varieties that need dedicated trellis support.
Watch For
Bush lima beans are the more practical choice for this interplanting - pole lima varieties will climb whatever's nearby, including corn stalks, which can work intentionally in a three-sisters-style arrangement but adds real weight and wind resistance to a corn stalk not bred to support a climbing vine the way traditional flint or dent corn varieties used in historical three sisters plantings are.
Frequently Asked Questions
Since lima beans and corn both want warm soil, should I direct-sow both on the exact same day?
Not necessarily. Even though their seasons genuinely overlap here, unlike with peas, lima beans germinate slowly and can sulk in soil that's only just warm enough for corn - waiting a week or so after corn goes in, once the soil has warmed further, often gives lima beans steadier germination without giving up much of the season-long overlap this pairing depends on.