Beans fix nitrogen that feeds the corn growing beside them, that season.
This claim only partly holds up. A good hunch A person has checked it against its sources.
The planner won’t plan around this claim. What is known instead is below.
What is actually known
Rhizobia in legume root nodules do fix atmospheric N. Most of it is incorporated into the legume's own tissue. Some does move to a neighboring non-legume the same season via direct root contact and rhizodeposition, but the amount is small (a few percent of the neighbor's N uptake) and does not meet a heavy feeder's demand. The bulk of the benefit arrives the following season, after residues decompose.
When this applies to a garden, Milpa says: Beans will improve this ground for next year. They will not feed your corn this year.
The evidence
Evidence: checked against 3 sources in the research-based literature.
The 3 sources
Most of the nitrogen converted by the beans will not be available to the corn and pumpkins the first year; the bean roots have to break down to release nitrogen. Corn is a heavy nitrogen [feeder].
N transfer rates of between 3.1 and 6.0% ... from soybean to maize
N transferred from soybean to maize account for 2.4%–3.3% of the N uptake of maize.
Plant teams that rest on it
- Blackberry hedge
- Currant ring
- Fruit tree ring
- Fruit tree ring (dwarf)
- Melon Sisters
- Milpa
- Sweet-potato milpa
- Three Sisters
Read next
- Do beans really feed the corn?The most repeated fact about the Three Sisters, that the beans fix nitrogen to feed the corn beside them, is half true, and the wrong half is the one people rely on. Here's what happens.
- What the evidence says about companion plantingMost companion-planting chart entries are tradition, and few were ever tested. Here's the short list of pairings that hold up, the famous ones that don't, and how to tell which is which.
How this rule has changed
Every change is dated, newest first. The full record, with each reason, is in the data download.
- Details updated
- Sources updated
- Wording made clearer
- Sources updated
- A person read the sources and confirmed it
- Added to the rules
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Cite this page
Milpa Gardens. “Beans fix nitrogen that feeds the corn growing beside them, that season.” Evidence grade: A good hunch. https://milpa.garden/rules/beans-fix-nitrogen-that-feeds-corn-growing/
A garden planner built on graded evidence. Every claim states its evidence grade and links its sources on the page. Cite it with the grade, and add the date you read it.
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How we grade evidence
- Well established
- The rule names its mechanism and is settled, by sources a person has read and checked or by plain arithmetic and geometry.
- Promising
- The mechanism is named and the literature backs it. A few questions are still open.
- A good hunch
- Plausible by its mechanism, but field studies are thin, so treat it as a lean.
- Contested
- The evidence points both ways, or no study has tested it, so the planner does not enforce it.
- Refuted
- The claim did not survive its sources. It is kept so the folklore can be answered.