Three Sisters: Corn, Beans and Squash Together

Why it matters

Native American growers planted corn, beans and squash together because each crop helps the others. Corn gives beans something to climb, bean roots host bacteria that add nitrogen to the soil, and big squash leaves shade the ground to hold moisture and smother weeds. It packs three crops into one patch.

Step by step

1. Wait for warm soil All three crops are killed by frost. Plant after your last frost, once soil is above 65°F, which is AgriLife's minimum for corn. Corn won't sprout below 50°F.
2. Build mounds Traditional Haudenosaunee hills were about 1 foot high and 2 feet wide, spaced about one step apart in rows.
3. Plant corn first Sow 4-7 corn seeds about 6 inches apart in the center of each mound, 1-2 inches deep. Pull soil up around the stalks as they grow.
4. Add beans when corn is 4-6 inches tall Plant 3-4 pole bean seeds in a ring about 6 inches out from the corn, then thin to the 3-4 strongest. Traditional growers planted beans 2-3 weeks after the corn.
5. Add squash around the outside At about the same time you thin the beans, plant squash around the outer ring or between mounds, 3-4 feet apart so the vines have room to run.
6. Feed and water Corn is a heavy feeder. Side-dress it when tassels start forming. Water deeply, since corn roots are shallow (12-18 inches), and the most critical times are planting, tasseling and ear fill.
7. Guard the squash from vine borers Cover young squash with floating row cover, burying the edges, then open it at bloom for bees. Check stems for sawdust-like frass, and slit stems to remove larvae.
8. Clean up after harvest Pull and destroy spent squash vines right away, and turn the soil in fall to expose overwintering borer pupae to weather and birds.

Key facts

• The system spread north from Mesoamerica and was practiced by the Haudenosaunee (Iroquois), Seneca, Cherokee and others. One source dates its adoption in North America to about 1070 AD (USDA National Agricultural Library).
• Corn: plant when soil is above 65°F, 1-2 inches deep. No germination below 50°F (AgriLife, Masabni).
• Snap beans: direct-sow when spring soil reaches 60-65°F (AgriLife).
• Beans drop blossoms above about 85-90°F, so plant early in spring (AgriLife).
• WVU Extension spacing: 4-7 corn seeds 6 inches apart, beans in a ring 6 inches out, squash 3-4 feet apart around the outer ring.
• Plant beans when corn is 4-6 inches tall (WVU), or 2-3 weeks after corn (traditional method cited by USDA NAL).
• Sweet corn needs about 20 inches of water a season for early varieties and 35 inches for late ones (AgriLife).
• Squash: soil pH 6.0-6.5, 5-6 seeds per hill about 1 inch deep, thinned to 3 plants at 3-4 inches tall (AgriLife EHT-041).
• Texas squash vine borer moths fly from as early as April-May to as late as November-December, with at least two overlapping generations a year (Texas A&M Urban Entomology).
• Borer larvae overwinter in soil up to 2 inches deep under the old plants.

Texas notes

• Pole bean varieties AgriLife lists for Texas: Kentucky Wonder, Dade, Northeaster and Romano Gold for snap beans, and King of the Garden, Florida Butter and Florida Speckled for pole limas.
• Squash types Texas A&M entomologists say borers find less attractive: Tatume, white bush scallop, acorn, summer crookneck, Dickinson pumpkin, green-striped cushaw, butternut and zucchetta. Cushaw and butternut are good vining 'sisters.'
• Average last frost (AgriLife): Houston about Feb 12, Austin about Mar 16, Amarillo about Apr 15. Plant once soil warms after that.
• Plant early. Texas heat above 85-90°F makes beans drop blossoms, and borer pressure builds through summer.
• Borer control from Texas A&M: Bt sprayed or injected into stems (reapply often, since sunlight breaks it down), or spinosad sprayed weekly in the evening. Spinosad is toxic to bees while wet.
• AgriLife EHT-041 notes larvae can't be controlled once inside the stem, so prevention matters most.
• Stagger squash plantings so young vines replace any lost to borers. If borers are bad every year, skip squash for a season.
• Pull out Johnsongrass nearby. Aphids carry maize dwarf mosaic virus from it to corn (AgriLife).