Corn, beans, and squash have been grown together for centuries in the Americas, and for good reason: they naturally work in concert with each other. Corn provides a growing support for the beans, which in turn provide nitrogen for the corn and squash. The large leaves of the squash provides shade that help to conserve moisture in the soil and control weeds. The seeds of each type of vegetable can also be saved from year to year, provided they are isolated from cross-pollination.
All three plants are heat lovers, so wait until the soil has warmed up in late spring when the soil is consistently 18°C (65°F) to direct sow. Start by planting the corn seeds 30cm (12") apart in as close to a grid shape as possible. Sow the bean seeds outside the perimeter of this grid. Sow the squash seeds at the corners of the grid so they are also 30cm (12") from the nearest corn seed.
Alternatively, start all the seeds indoors 3-4 weeks before planting out, and aim for the same kind of spacing. It may look sparse at first, but these are fast growing plants. They are all heavy feeders, so they do best in rich soil amended with organic fertilizer.
Latin
Bean: Phaeolus coccineus
Corn: Zea mays
Squash: Cucurbita maxima
Difficulty
Moderately easy, but challenging due to space requirements.
Season & Zone
Season: Warm season
Exposure: Full-sun
Timing
The Three Sisters are heat lovers, so wait until the soil has warmed up in late spring when the soil is consistently 18°C (65°F) to direct sow. If the soil is not warm enough, seeds may rot before sprouting. Warmer soil improves germination. If spring weather is cold, plant indoors with bottom heat, and transplanting once weather warms. Seeds should germinate in 7-14 days. Alternatively, start all the seeds indoors 3-4 weeks before planting out.
Starting
Start by planting the corn 30cm (12") apart in a dense block of at least 4 rows. Sow the beans outside the perimeter of this grid. Sow the squash at the corners of the grid so they are also 30cm (12") from the nearest corn. It may look sparse at first, but these are large and fast-growing plants.
Growing
All three plants are heavy feeders, so they do best in rich, well-drained soil amended generously with organic fertilizer. For more detailed information, see:
Days to Maturity: From direct sowing.
Seed Info
In optimal conditions at least 75% of seeds will germinate. Usual seed life: 2-3 years.