Three Sisters
A polyculture - the species are claimed to help each other, and each claim below names its mechanism.
Haudenosaunee and widespread Indigenous North American polyculture.
Space it needs
At least 4 m². A bed smaller than that does not get this guild quietly substituted for something else — the planner greys it out, says why, and offers the nearest adaptation that does fit.
If your bed is smaller: Three Sisters (Small Bed) (1.5 m²).
Variations on it: Four Sisters (4 m²).
Between seasons
Nothing is left living in the bed over winter; the whole planting is re-established.
What it claims
squash foliage suppresses weeds and retains soil moisture
Mechanism: Light interception at the soil surface; reduced evaporation.
Evidence: confirmed against 2 sources in the research-based literature.
the 2 sources
UMN Extension, 'Mulching for soil and garden health', extension.umn.edu/managing-soil-and-nutrients/mulching-soil-and-garden-health (read 2026-07-11): mulch 'Suppresses weeds'; 'Studies show that mulch reduces evaporation from the soil surface and helps soil hold water.'
Cornell Cooperative Extension (Warren Co. Master Gardener), 'Creating a Three Sisters Garden', warren.cce.cornell.edu/gardening-landscape/warren-county-master-gardener-articles/creating-a-three-sisters-garden (read 2026-07-11): 'The large, prickly squash leaves shade the soil, preventing weed growth' — the living-mulch role in Three Sisters.
squash spines and sprawl deter some vertebrate pests
beans fix nitrogen available to corn in-season
Evidence: confirmed against 3 sources in the research-based literature.
the 3 sources
Univ. of Arkansas Extension, 'Creating a Three Sisters Garden', uaex.uada.edu (read 2026-07-11): '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].'
Hupe et al. 2021, Sci Rep 11:11424, 'Evidence of considerable C and N transfer from peas to cereals via direct root contact but not via mycorrhiza', pmc.ncbi.nlm.nih.gov/articles/PMC8169652 (read 2026-07-11): reports 'a mean N transfer rate of 8.4%, with a range of 2.7 to 22.5%, ... from N2-fixing legumes to non-N2-fixing mycorrhizal cereals' and 'N transfer rates of between 3.1 and 6.0% ... from soybean to maize'.
'Nitrogen uptake and transfer in a soybean/maize intercropping system in the karst region of southwest China', pmc.ncbi.nlm.nih.gov/articles/PMC5648690 (read 2026-07-11): 'N transferred from soybean to maize account for 2.4%–3.3% of the N uptake of maize.'
Roles
A role is filled by whatever satisfies its predicate, not by a fixed species list. The canonical filler is the default; the alternatives are priced.
Support
- Canonical: Corn
- Alternatives: Sunflower
- What the alternative costs: Sunflower can carry the beans, but it is a heavy nitrogen feeder that competes with the fixer and casts shade, and it needs a ~30-day head start or the vines pull it down.
Fixer
- Canonical: Common Bean
- Alternatives: Runner Bean, Cowpea, Lima Bean
Cover
- Canonical: Summer Squash
- Alternatives: Butternut, Winter Squash, Sweet Potato, Cucumber
What it costs the ground
Rotation history attaches to the ground, not the bed, so this is what the planner remembers about this patch after the guild comes out.
- Grasses: full load
- Legumes: full load
- Cucurbits: full load
A belief this raises
Companion planting charts encode real relationships.
Most companion planting advice you'll find online is folklore. Here's what we can actually defend, and why.
what is actually known
The bulk of the modern companion-planting canon descends from early-20th-century biodynamic and anthroposophical writing, propagated through mid-century popular gardening literature. Individual pairings are rarely trialled. A minority have real named mechanisms — volatile masking, living mulch, insectary provisioning — and are recorded here as a good hunch. Most have nothing.
what this rests on - one pointer
history of the companion planting literature
Rules that gate it
Corn requires a block of at least 4 rows (roughly 12 plants) for adequate kernel set.
Mechanism: Maize is wind-pollinated and protandrous. Tassels shed pollen that must land on silks of neighbouring plants. Below roughly 12 plants in a block of at least 4 rows, insufficient pollen reaches enough silks; each unfertilized silk is one missing kernel.
Evidence: confirmed against 4 sources in the research-based literature.
the 4 sources
UMN Extension, 'Growing sweet corn in home gardens', extension.umn.edu/vegetables/growing-sweet-corn (read 2026-07-11): 'Always plant corn in blocks of at least four rows. Corn planted in a single row will have much of its pollen blown out of the row, and will produce ears that have blank areas where kernels did not form.'
NC State Extension, 'Organic Sweet Corn Production' (Horticulture Information Leaflets), content.ces.ncsu.edu/organic-sweet-corn-production (read 2026-07-11): 'Corn is wind-pollinated and should be planted in blocks of at least 4 rows for good pollination to occur.'
UMD Extension, 'Growing Sweet Corn in a Home Garden', extension.umd.edu/resource/growing-sweet-corn-home-garden (read 2026-07-11): 'Plant in blocks of at least three to four short rows, rather than one or two long rows, to ensure good pollination; minimum of three rows side by side (preferably four rows).'
Clemson HGIC 1308, 'Sweet Corn' (updated 2023-01-23), hgic.clemson.edu/factsheet/sweet-corn (read 2026-07-11): 'This crop is wind-pollinated; therefore, plant in blocks of several rows rather than 1 or 2 long rows to ensure full ears.'
remedy
Plant in a block of at least 4 rows, or omit corn and substitute a trellis.