Milpa Gardens

Four Sisters

A polyculture - the species are claimed to help each other, and each claim below names its mechanism.

Contested and regional. The fourth sister is variously given as sunflower, Rocky Mountain bee plant, or amaranth, depending on nation and source. Do not present a canonical version.

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.

Adapted from Three Sisters.

Between seasons

Nothing is left living in the bed over winter; the whole planting is re-established.

What it claims

insectary draws pollinators and predatory insects

A good hunch

Mechanism: Nectar and pollen resource provisioning.

Evidence: confirmed against 1 source in the research-based literature.

the source

UC Statewide IPM Program (UC IPM), 'Insectary Plants', ipm.ucanr.edu/environmental-protection-and-pesticide-stewardship/insectary-plants (read 2026-07-11): 'Insectary plants are those grown to attract, feed, and shelter insect parasites (parasitoids) and predators to enhance biological pest control. Insectary plants provide nectar and pollen, which the adults of many natural enemy species need to consume.' (UC IPM also notes 'insectary plants may not always help' suppress pests — consistent with the grade-C 'reasonably supported' framing.)

sunflower as fourth sister competes for N and casts shade

Promising

Mechanism: Allelochemicals in Helianthus residue and root exudate.

Evidence: confirmed against 1 source in the research-based literature.

the source

'The Allelopathic Activity of Aqueous Extracts of Helianthus annuus L. ... on Germination, Development, and Physiological Indices of Pisum sativum L.', PMC10180669, pmc.ncbi.nlm.nih.gov/articles/PMC10180669 (read 2026-07-11): 'If a sensitive test plant is exposed to allelopathic compounds, its seed germination and seedling growth are reduced'; 'Aqueous extracts of various organs of sunflower significantly suppress the growth of weeds ... and agricultural plants.' Effect was concentration-dependent (stimulatory at low concentration, inhibitory at 75%), consistent with the 'modest' effect_size. NOTE: this study used pea (large-seeded); the small-seeded/direct-sown scoping is the corpus's operationalization (small seeds have less reserve to overcome inhibition; transplants bypass the germination window), not a claim from this source.

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

Fixer

Cover

Insectary

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.

Rules that gate it

Corn requires a block of at least 4 rows (roughly 12 plants) for adequate kernel set.

Well established · fatal if ignored → block

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.

See this rule in the planner

All guilds